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Useful Knowledge: 4th ed. Minerals. Vol 1 of 3

Frontispiece to Vol. I. see Page [237].

Comparative Height of Mountains, Cities and Lakes
British Islands Continent of Europe Islands not British Asia America
(Click on image to see a larger version.)
J. Shury sculp.

USEFUL KNOWLEDGE:

OR

A FAMILIAR ACCOUNT

OF THE

VARIOUS PRODUCTIONS

OF

Nature,

MINERAL, VEGETABLE, AND ANIMAL,

WHICH ARE CHIEFLY EMPLOYED FOR THE USE OF MAN.

Illustrated with numerous Figures, and intended as a Work both of Instruction and Reference.

BY THE

Rev. WILLIAM BINGLEY, AM. FLS.

LATE OF PETERHOUSE, CAMBRIDGE, AND AUTHOR OF ANIMAL BIOGRAPHY.

IN THREE VOLUMES.

VOL. I. MINERALS.

FOURTH EDITION.

LONDON: PRINTED FOR BALDWIN, CRADOCK, AND JOY;

HARVEY AND DARTON;

AND C. AND J. RIVINGTON.

1825.

C. Baldwin, Printer,

New Bridge-street, London.

PREFACE.

The mode in which instruction has hitherto been conveyed, on the peculiar subjects of the present work, has chiefly been by small books, in question and answer, denominated catechisms. But such, however respectable in themselves, or however advantageous for children, are wholly insufficient for persons who are in search of extended knowledge, and desirous of furnishing their minds with useful information.

On these subjects there has not hitherto been published any work in which they are collectively to be found; nor could a knowledge of them be obtained but by the consultation of many and expensive writings. That they are generally important to be known will not probably be denied.

It has consequently been the object of the author to compress all the interesting information that could be obtained respecting them, within as narrow a compass, and at the same time to render this information as entertaining, and as devoid of technical words and phrases, as possible.

The scheme of the work will, it is hoped, be found sufficiently simple. The passage in smaller characters at the head of each article, is in general so arranged as to reply to the questions, “What is?” “What are?” or “How do you know?” For instance: “What is flint?” (See Vol. I. p. [53].) The answer will be found thus: “Flint is a peculiarly hard and compact kind of stone, generally of smoke-grey colour, passing into greyish white, reddish, or brown. It is nearly thrice as heavy as water, and, when broken, will split in every direction, into pieces which have a smooth surface.” The author is aware that, in many instances, the definitions are defective: but this has, in general, arisen from a necessity of rendering them short, and at the same time of using such terms as would be likely to convey information to the minds of persons who have had no previous knowledge of the systems of natural history.

After the definition, a further illustration sometimes follows; and in the large characters will be found a brief detail of the history and uses of the object described. The articles are numbered, for the greater convenience both of reference and explanation, but particularly the latter. Thus, under the explanation of Carbon, it is stated that “in combination with oxygen ([21]) it forms carbonic acid ([26]), and that it is the chief component part of pit-coal ([217]), petroleum ([213]), and other bituminous substances.” By a reference to the numbers inserted, each of the words, against which they stand, will be explained: whilst at least three of them would otherwise have been incomprehensible by the generality of unscientific readers.

It must be remarked that the reader will not here find an account of every production of nature, which is employed for the use of man, nor even all the uses of such objects as are described. The most important of the productions, and the principal of the uses, are all that he trusts can reasonably be required in a work of the present extent. On this ground it is that a great number of animals, which are in request only for food, have been wholly omitted.

The figures that are inserted have been drawn upon as small and economical a scale as was compatible with a sufficiently accurate representation of the objects to which they relate. If the reader be desirous of reference to further illustration, he will derive much satisfaction from the invaluable figures of Mr. Sowerby in his British and Exotic Mineralogy, and English Botany, and Woodville’s Medical Botany; as well as from those in Dr. Shaw’s General Zoology, and Bewick’s Histories of Quadrupeds and British Birds. There are also many figures of useful animals in the author’s own work, entitled “Memoirs of British Quadrupeds.”

ADVERTISEMENT

TO THE

THIRD EDITION.

Since this work was first printed, the author has made in it considerable improvements. The first volume, particularly, contains many additional articles, and more than half of it has been re-written. The plates also have been re-engraved. For the plate of the mountains a new drawing has been made, that the scale might be extended, and many particulars might be introduced which before were omitted. For the plates of vegetables every drawing has been corrected; and, in place of such figures as were most defective, new ones have been inserted.

Charlotte-street, Bloomsbury,

London, 1st March, 1821.

EXPLANATION OF THE PLATES
OF THE
FIRST VOLUME.

FRONTISPIECE.

This is explained in pages [236], [237].

PLATE I.

PLATE II.

CRYSTALS, &c.

PLATE III.

SECTION OF ROCKS.

I. Primitive Rocks.

II. Secondary Rocks.

1. Transition Rocks.

2. Floetz Rocks.

III. Alluvial Deposits.

The BINDER is desired to insert all the Plates, except the Frontispieces, immediately after the Explanations in the respective Volumes.

Pl. 1. Vol. I.
J. Shury. sculp.
Sections of Strata &c.

Pl. 2. Vol. I.
CRYSTALS &c.

Pl. 3. Vol. I.
Section of Rocks. J Shury sculp.

USEFUL KNOWLEDGE.

MINERALS.

INTRODUCTION.

1. Minerals are natural bodies destitute of organization and life: and Mineralogy is that branch of natural science which treats of the properties and relations of such bodies.

MINERAL DEPOSITS.

2. If we penetrate beneath the surface of the earth, we observe there a very remarkable arrangement. Instead of a generally uniform appearance, as we see on the surface, we pass through divers substances, as clay, gravel, sand, and numerous others, deposited in beds or strata of various thickness, from a few inches to a great many feet ([Pl. I. Fig. 1]). These lie, for the most part, nearly horizontal: but in some instances, particularly in mountainous countries, they take different degrees of inclination; and, in places where the country consists of gently sloping hills and vales, the beds have a waving or bending form ([Pl. 1, Fig. 3]). The strata of which the earth is composed, as deep as the curiosity or the necessities of mankind have induced them to explore, satisfactorily demonstrate the wisdom which has been displayed in the arrangement of materials requisite for the use of men and animals.

The first layer is frequently a rich, black mould, formed almost wholly of animal and vegetable remains. This yields sustenance to the vegetable productions; and thereby becomes the actual, though not the immediate, support of the whole animal creation.—Beneath this is often found a thick bed of clay, that furnishes to man a substance of which to make bricks, tiles, various kinds of pottery, and innumerable other articles for the comfort of social life.—Next are deposited vast beds of gravel, that are of use in numerous points of view.—Underneath this are the infinitely varying strata of sandstone, limestone, &c. which not only serve for the construction of buildings, and for other important purposes, but also frequently surround mines which contain the valuable metals.—Beneath a slaty stratum are usually discovered those immense beds of coal so requisite for the comfort, and, in some situations, even for the existence of man.

These strata, it is true, are not always found together, nor are they always discovered in the same order; but the statement will suffice to show the general nature of their arrangement.

3. Minerals are sometimes observed in detached masses of various size, and situated at various depths in the earth ([Pl. I, Fig. 1]).

4. They are also found in a kind of natural clefts which cross the regular mineral beds or strata in different directions ([Pl. I, Fig. 1, a], [Pl. I, Fig. 4, b]). When these contain metallic ores, they are styled veins; but when they contain only stony or earthy matters, the miners call them dykes. They vary much both in magnitude and length. Six thousand feet are considered an unusual length for veins, though, in some instances, veins have been traced upwards of four miles. Few veins extend more than 1200 feet below the surface of the mountains in which they are situated. They are usually much inclined; but they sometimes descend in a direction parallel with the beds of rock in which they occur.

5. At the places where dykes or veins pass through the earth, they occasionally disjoint the strata in a very singular manner ([Pl. I, Fig. 4]). Some of the coal strata, for instance, are thrown down or raised on one side of a dyke upwards of a hundred yards; and the miner, after penetrating through this dyke, instead of finding the same coal again, meets, on the opposite side, with beds of stone or clay. Hence he is frequently at a loss how to proceed in searching for the coal of which he is in pursuit; and hence it is that to such dykes the peculiar name of faults has sometimes been given.

6. In England the metallic ores are generally found in veins, that form a considerable angle with the regular strata. This in Cornwall is uniformly the case. And it is remarkable, concerning the veins of tin and copper of that county, that they run in a direction nearly east and west; whilst the dykes, or veins of other substances, run for the most part north and south.

7. The thickness of veins, and the quantity and quality of the ores they contain, differ in every mine. Some are only a few inches wide, whilst others extend to the width of several feet. The vein at Dalcooth mine, in Cornwall, varies from two or three to forty feet and upwards; and, in some parts, it contracts so as to be little more than six inches across.

8. In Cornwall the first traces of tin and copper are usually found at the surface of the ground, and thence to the depth of 80 or 100 feet beneath; and it is said that no miner has ever yet seen the bottom of a vein, although several have been wrought to the depth of more than 1000 feet. The veins of these metals have, in some instances, been worked to the length of three or four miles.

9. It is frequently observed that metallic veins are separated, from the substances they intersect, by a thin wall, or lining, of minerals different from these substances, and also by a layer of clay on each side of the vein. It is also remarked that the same substance which forms the outer coat of the vein is often intermixed with the ore, or forms layers alternately with it. This has usually the denomination of matrix or gangue.

10. There are few mines of any considerable depth that would not be flooded with water from internal springs were not means adopted for drawing off this fluid. The steam engines that are employed for this purpose in some of the Cornish mines are so powerful as to discharge incessantly, both by night and day, a quantity of water, equal to at least 1000 gallons, or near twenty hogsheads, every minute.

SYSTEMATIC ARRANGEMENT OF MINERALS.

11. To a superficial observer, perhaps nothing would appear more easy than to describe a mineral. This, however, is by no means the case. The same general appearance sometimes prevails in substances that are very different from each other; and the same stone, in its different states, is often extremely varied in its appearance. To these difficulties it must be added, that the combinations of mineral substances are multiplied to a great extent. A little application, however, particularly if the student be possessed of a collection of arranged and named specimens, which he will have no difficulty in procuring at a reasonable price, will enable him to overcome all the obstacles that otherwise might impede his progress in beginning to acquire a knowledge of this interesting science.[^[1]]

12. The most simple and natural division of minerals is into four classes, of, 1. Stones; 2. Salts; 3. Combustibles; and, 4. Metals; and the following table, which has chiefly been arranged from the system of Werner, the well-known German mineralogist, will exhibit a tolerably correct outline of the classification of these substances. To reduce the whole within the compass of a single page, many of the families, however, have necessarily been omitted.

[1]. Such collections are supplied by Mr. Mawe, No. 149, Strand, London. His terms, for collections containing from 100 to 200 specimens, are 5 guineas; from 200 to 300 specimens, 10 guineas; and from 300 to 400 specimens, 15 guineas. For collections containing from 350 to 400 specimens, more select, and comprising a better suite of precious stones, he charges from 20 to 30 guineas; and for larger collections, from 50 to 100 guineas. At the particular request of the author, Mr. Mawe has arranged a few collections of minerals, and numbered them in such manner as to correspond with, and illustrate the present volume.

13.To complete a general view of the different productions of the mineral kingdom, it is requisite to subjoin a tabular arrangement of the various kinds of rocks.

14. For the purpose of ascertaining the names and characters of minerals, attention must be paid to their form, surface, lustre, fracture, or the appearance of their internal surface when broken; structure, transparence, streak, or the mark left when scratched by any hard body; stain, or trace left when rubbed upon paper; cohesion, whether solid, friable, or fluid: hardness, or the resistance which they oppose when scratched; tenacity, or the resistance which they oppose to the stroke of a hammer; flexibility, or their property of bending without breaking; feel, or the sensation communicated by their surfaces when handled; smell, taste, adherence to the tongue, sound, specific gravity, or weight in comparison with that of water; colour and electricity.

15. To ascertain the chemical properties of minerals, one of the most important instruments is the blow-pipe. This is a tube which terminates in a cavity as fine as a small wire, and through which the air is forced, and made to play upon the flame of a candle. The flame is thus concentrated, and directed against small particles of the mineral to be examined, which is placed upon a bit of charcoal in a spoon of platina or silver. The air is forced into the blow-pipe by the mouth of the person using it, or by bellows attached to it for that purpose. Under this operation we have an opportunity of trying the action of other bodies upon minerals at a very high temperature; and the properties which these experiments bring into view enable us, in many cases, to ascertain, not only the nature, but even the component parts, of minerals.

SIMPLE MINERAL SUBSTANCES.

16. As a necessary introduction to the study of minerals, it is requisite to describe, in a brief manner, such simple substances as form their constituent parts. Few of these, it is true, are to be found in a separate, uncombined state; yet that they do exist, and that they are to be obtained from the minerals with which they are united, we have the proof of every day’s experience.

UNCONFINABLE FLUIDS.

17. There are some kinds of unconfinable fluids, the existence even of which is manifested only by their contact with other bodies, or becoming separated from them. They are of a nature too subtile to be collected or confined in our vessels for the purpose of examination, and the investigation of their properties has consequently been attended with peculiar difficulty. Those at present known are caloric, light, electricity, and magnetism; but of these the first only is immediately connected with the subjects of our present investigation.

18. Caloric.—Every one is acquainted with the different sensations of heat and cold. That matter which produces on our bodies the sensation of heat has the name of Caloric; heat being only an effect, of which caloric is the cause. This is extended in a greater or less degree through the whole extent of space, and penetrates into the interior of even the most solid bodies: in so doing it expands the particles of which they are composed, augments their bulk, and diminishes their solidity. The sun is the principal fountain from which the earth is supplied with this fluid; and it passes thence to us at the rate of 12,000,000 of miles per minute. The defect of caloric in any substance occasions the sensation called cold.

Were the world deprived of caloric, every species of organized being would, from that moment, cease to exist. It is the cause of all fluidity: to it every production of the earth has been most essentially indebted, even for its form and structure; and in no respect do the power and goodness of the Almighty appear more conspicuous than in the creation, dispersion, and continuance, of this most subtile and astonishing fluid.

19. All the various substances with which we are acquainted must be considered either as solid or fluid. Every substance is defined to be a solid in which the parts are so united or connected that it requires an external force to separate them. A fluid, on the contrary, is a body the parts of which are so loosely connected that they not only yield easily to any force impressed upon them, but also move freely amongst each other; and every fluid is a combination of caloric with some other substance.

20. Fluids are of two kinds: one of these, called liquids, have, when at rest, a smooth and distinct surface, and are distinguishable both by the sight and touch; the other, denominated gas, or gaseous fluids, have the appearance of air, and are not perceptible either to the sight or touch, except under certain circumstances. The latter are principally oxygen ([21]), azote or nitrogen, and hydrogen ([45]). We shall at present have occasion to speak only of the first.

GASEOUS FLUIDS.

21. Oxygen, like caloric, is a fluid never found in an uncombined state. It forms one of the component parts of the air that we breathe, and of the water we drink; but it approaches nearest to a state of purity in combination with caloric ([18]), when it has the name of oxygen gas. It was formerly called vital air, because no breathing animal can live for a moment in any air or gas which has not in it a mixture of oxygen; every kind of combustible burns with great splendour in it, and without it ceases to burn. It unites with a great number of substances, and changes both their appearance and properties in a very remarkable manner. Of the metals it entirely destroys the metallic lustre, and gives them an earthy form and texture. Substances in this state have the name of oxides.

Lead, for instance, combined with oxygen becomes the well-known red and heavy substance used by painters, under the name of minium or red lead ([239]). This, if deprived of its oxygen, loses its red colour, and returns to its former metallic state. Some of the metals are oxidized by merely being exposed to moisture. Thus the rust which is so readily contracted by iron is an oxide of that metal, produced by its attracting oxygen from the air or from water.

ACIDS.

22. It is one of the most remarkable properties of oxygen to impart to most of those bodies called acids their peculiar character of acidity. Oxygen does not itself possess the properties of an acid, nor is it an essential ingredient in all acids, though it is the acidifying principle in the greater number of them.

23. Acid is a word originally synonymous with sour. It has, however, been gradually extended in its signification, and now comprehends all substances possessed of the properties of exciting upon the tongue the sensation called sour; of changing the blue colours of vegetables to red; of uniting with water in almost any proportion; of combining with alkalies ([42]), metallic oxides, and earths, and of forming with them certain compounds called salts.

24. Sulphuric Acid, or Spirit of Vitriol, as it is commonly called, is a liquid of a somewhat oily consistence, transparent and colourless as water, formed by a combination of oxygen ([21]) with sulphur ([46]). Like other acids, it never occurs in nature in a pure state, for it can no sooner be formed than it unites with earths ([31]), alkalies ([42]), or metals, and forms, with them, several well-known salts, which have the name of sulphats. Thus alabaster ([192]) and Epsom salts ([199]) are respectively formed by an union of sulphuric acid with lime and magnesia, and are denominated by chemists sulphat of lime and sulphat of magnesia. In like manner, blue vitriol ([209]) is sulphat of copper; green vitriol ([208]), sulphat of iron; and white vitriol ([210]), sulphat of zinc.

25. Phosphoric Acid is produced by a combination of oxygen ([21]) with phosphorus ([47]); and, when obtained in a state of purity, is not a fluid, but a white and flaky substance. This acid, when combined with mineral productions, forms those salts which have the name of phosphats. It is very soluble in water; and, in dissolving, makes a hissing noise, similar to that produced by plunging hot iron into water.

26. Carbonic Acid is a compound of oxygen ([21]) and carbon, or pure charcoal ([48]): and in a state of gas ([20]) it forms a constituent part of the atmospheric air. It is also emitted in great abundance from wine, beer, and other liquors, in a state of fermentation, and is sometimes found in the lowest parts of mines, where it is known to the miners by the name of choke damp, from the circumstance of its immediately extinguishing flame, and suffocating all animals that are immersed in it. This gas, which was formerly called by chemists fixed air, is about twice the weight of common air. In combination with lime it forms chalk, marble, and limestone; and it constitutes part of several other mineral substances, which are thence denominated carbonats.

27. Fluoric Acid is a gas of very singular nature, which is held in combination with lime, in the Derbyshire or fluor spar ([194]); and may be separated from it by pouring sulphuric acid, or spirit of vitriol ([24]), upon powdered spar, in a leaden vessel called a retort, and applying to it a gentle heat. The salts formed by fluoric acid have the name of fluats.

28. The Boracic is a peculiar kind of acid, which, in combination with soda ([200]), forms the substance that we import from the East Indies under the name of borax ([204]). When extracted from borax this acid does not assume the form of a fluid, but appears in thin six-sided scales or flakes, of white colour, which adhere slightly together, and feel somewhat greasy in handling. To the taste it is at first sour, then bitterish; and at last it leaves an agreeable sweetness on the palate.

29. Muriatic Acid is a gas formed by the combination of oxygen ([21]) with some base that is not yet known. It is an invisible and elastic fluid, which, in mechanical properties, resembles common air, and has a pungent and very peculiar smell. This gas unites with alkalies ([42]), earths ([31]), and the oxides ([21]) of metals; and with them forms the compounds called muriats, of which common salt, or muriat of soda ([202]), is one of the principal. The liquid muriatic acid, or muriatic acid gas combined with water, is frequently denominated spirit of salt ([202]).

30. Nitric Acid is a compound of oxygen and azote, or nitrogen, in the proportion of twenty-five parts, by weight, of the latter to seventy-five of the former. It is one of the constituent parts of nitre, or saltpetre ([206]); and, in a pure state, is transparent and colourless, like water. By the action of light, however, it soon becomes yellow; and, if exposed to the air, it emits yellow fumes, which even tinge the air of the same colour. To the taste it is extremely acid. It dyes the skin a yellow colour, which is very difficult to be removed; and it is so corrosive as to destroy almost every substance into which it penetrates. If poured upon oils, it sets them on fire. With various bases it forms compounds called nitrats. This acid, which hitherto has never otherwise been obtained than mixed with water, is chiefly known in commerce by the name of aqua fortis ([206]).

EARTHS.

31. The solid contents of the globe are composed of several elementary substances, amongst which have been enumerated no fewer than nine different kinds of earth:

1. Silex.

2. Alumine.

3. Zircon.

4. Glucine.

5. Yttria.

6. Barytes.

7. Strontian.

8. Lime.

9. Magnesia.

These, when freed from foreign admixture, are, for the most part, of white colour, not soluble in water, not combustible, and do not exceed four times the weight of water.

32. The whole of these earths have, till lately, been considered simple and uncombined substances; but, by the discoveries of Sir Humphrey Davy, it has been ascertained that four of them have a metallic basis, and are in fact metallic oxides, or compounds consisting of a metal united with oxygen ([21]). These, which have the same affinity with their respective bases as rust has to iron, are silex, lime, barytes, and alumine. Until, however, some further light be thrown upon their nature and constitution, they must continue to hold their former situation of simple earths.

33. Silex, or Siliceous Earth, is the basis of all substances known by the name of quartz and silex ([76]). In a state of nature it has never been found pure; but, in combination with other substances, it abounds in almost every country of the globe. Common flint ([90]) contains ninety-seven parts in a hundred of silex: it consequently has given its name to this earth, silex being the Latin word for flint. When purified it is a white powder, the particles of which are harsh to the touch, as if they consisted of very minute grains of sand. It is not quite three times as heavy as water, and has neither taste nor smell. Water will not dissolve it, nor any kind of acid, except fluoric. Sir H. Davy has discovered it to have a metallic basis, to which he has given the name of silicium.

34. Alumine is a kind of earth, so called from its forming the basis of alum ([197]). It is soft, compact, and tenacious; about twice the weight of water, and, when breathed upon, has a smell which is peculiar to all clayey productions. In the fire it shrinks, and becomes so hard as even to yield sparks when struck against steel. It readily absorbs water, and is dissolved by most acids. Some writers state that pure alumine has been discovered in a native state near Halle, in Germany. It is found in a crystallized form, and nearly in a state of purity, in the Oriental ruby and sapphire. The name of argil, or clay, has sometimes been applied to it; but, in mineralogy, this name has usually been given to a mixture of alum, quartz, and other substances. Sir H. Davy has obtained from alumine a metallic basis, called aluminum.

35. Zircon, when freed from those substances with which it is combined, is a white and somewhat rough powder, insipid to the taste, insoluble in water, and about four times as heavy as that fluid. It is found in the two kinds of precious stones called jargoon and hyacinth, and has not hitherto been applied to any useful purpose.

36. Glucine is a kind of earth of peculiar nature, which is found in the emerald and beryl, and, when purified, forms a soft and white powder, without smell, and of sweetish taste. To the last of these qualities it is indebted for its name, which is derived from a Greek word signifying sweet. It is somewhat unctuous to the touch, and about three times as heavy as water. The uses of this earth, whatever they may be, are not known.

37. Yttria is an earth which, among other particulars, differs from glucine by its weight, as it is nearly five times heavier than water. In a natural state it occurs as the basis of a black Swedish mineral, called gadolinite. When cleansed, by chemical process, from all its impurities, it is a fine, white, and inodorous powder.

38. Barytes is a white, porous, and very heavy earth, which can only be obtained pure by chemical process. It is easily reduced to powder, and is soluble in all kinds of acids. To the taste it is harsh and caustic; and, if taken into the stomach, proves an extremely virulent poison. In some respects it agrees with the alkalies ([42]), particularly in its property of changing blue vegetable colours to green, and in corroding, like them, though with less energy, all kinds of animal substances. From these circumstances it has sometimes been denominated an alkaline earth. Saturated with sulphuric ([24]) and carbonic acid ([26]), it constitutes the minerals denominated sulphat and carbonat of barytes ([196]). It has been discovered to have a metallic base, which is called barium.

39. Strontian is an earth which, like barytes, is not found otherwise than in combination with sulphuric and carbonic acids. It occurs in various parts of the world, and, when purified, forms a porous mass of greyish white colour, acrid taste, and somewhat alkaline nature. This earth converts vegetable blue colours to green, but does not act so strongly on animal bodies as barytes, nor is it poisonous, like that substance.

40. Lime, the basis of all those substances which are denominated calcareous, is only to be obtained in a state of purity by artificial process. Combined with carbonic acid ([26]) it forms limestone ([140]), chalk, and marble; all of which are capable of being converted into lime by burning. Lime may also be obtained from oyster and other sea shells. When pure, it is of white colour, and moderately hard substance, though it is easily reducible to powder. Its taste is burning and acrid; and, like the alkalies, it changes vegetable blue colours to green. It has likewise the property of corroding and destroying animal substances. Lime, when pure, absorbs water rapidly, becomes hot, and falls into powder. Even if exposed to the open air it gradually attracts moisture, and assumes a powdery form; soon after which it becomes saturated with carbonic acid ([26]) from the atmosphere, and is thereby again converted into carbonat of lime ([140]). It occurs abundantly in almost every country, but always in combination with some acid, carbonic ([26]), sulphuric ([24]), boracic ([28]), fluoric ([27]), or phosphoric ([25]). This substance has a metallic basis, which has been denominated calcium.

41. Magnesia is a light and perfectly white kind of earth, of soft powdery appearance, without taste or smell, and somewhat more than twice as heavy as water. It is not found in this pure state in nature, but may be prepared from Epsom salt, which consists of magnesia in union with sulphuric acid ([24]). The slightly acrid taste that is perceptible in the magnesia used in medicine arises from a portion of lime which it contains. This substance does not dissolve in water, but is soluble in every kind of acid. It has the property of changing delicate blue colours to green.

ALKALIES.

42. Alkalies are substances which enter into the composition of several kinds of minerals, and are known by their property of changing the colour of blue vegetable juices to green, and by a peculiarly acrid, caustic, and nauseous taste, which it is impossible to describe, but which, after it has been once experienced, will easily be recollected. Alkalies corrode and dissolve animal substances, and unite with oil and fat in such manner as to form the well known compound called soap. They readily dissolve in water; and, when mixed with acids, form what have been denominated neutral salts.

43. The alkalies at present known are three in number; potash ([205]), soda ([200]), and ammonia ([207]). Of these the two former, although till lately they have been considered simple substances, have been shown by Sir H. Davy to have metallic bases.

SIMPLE COMBUSTIBLES.

44. By this term we are to understand all those mineral substances, capable of combustion, which have not been discovered to consist of more than a single component part. They are four in number; hydrogen, sulphur, phosphorus, and carbon.

45. Hydrogen, as its name imports, is a principal constituent part of water; for, singular as it may appear, that well-known fluid is formed by a combination of two species of air or gas, called hydrogen and oxygen ([21]), and in the proportion of about fifteen parts of the former and eighty-five parts of the latter. This gas had formerly the denomination of inflammable air, and has long been known in mines under the name of fire-damp. It is about twelve times lighter than atmospheric air. When pure it soon destroys such animals, and extinguishes all such flaming substances, as are immersed in it. Mixed with atmospheric air, it explodes with great violence on the application of any ignited body.

46. Sulphur is a simple combustible substance, of yellow colour, which is found pure, or native, in several parts of the world, and is sufficiently familiar to us under the name of brimstone ([211]). It strongly attracts oxygen ([21]), and is thereby converted into sulphuric acid ([24]). It frequently occurs in combination with mineral substances, such as arsenic, antimony, copper, and other metallic ores.

47. Phosphorus is a combustible substance which, when pure, somewhat resembles bees’-wax both in colour and consistence; and, when exposed to the air under the usual temperature of our atmosphere, is luminous in the dark, and has a smell somewhat resembling that of garlic. It is so combustible that, when melted, it should be kept under water, as it cannot be exposed to the air during this process without great risk of catching fire. This substance is not known in a native state; and the whole of what is used in philosophy and commerce is obtained by different artificial processes. In union with oxygen ([21]) it becomes converted into an acid, called phosphoric acid ([25]), and, under this form, in conjunction with lime, it constitutes the bones of men and animals. The greater part of the phosphorus of the shops is obtained from bones.

48. Carbon is a name given to the pure inflammable part of charcoal. It is abundantly diffused throughout nature, for it enters into the composition of several minerals, and of all vegetable and animal bodies. The purest form under which carbon is known to exist is in the diamond ([50]). It may, however, be obtained sufficiently pure, for all common purposes, by burning a piece of wood, covered with sand, in a vessel called a crucible. In combination with oxygen ([21]) it forms carbonic acid ([26]). Carbon is a chief component part of pit-coal ([217]), petroleum ([213]), and other bituminous substances.

CLASS I.—STONES.

ORDER I.—EARTHY STONES.

I. HARD: those which scratch Glass.

49. OF GEMS IN GENERAL.

Gems, or precious stones, as they are frequently called, are, for the most part, transparent, and have a vitreous or glassy appearance. Their different colours are occasioned by metallic oxides ([21]) of various kinds, with which they are impregnated. Some writers have classed them by their colours, but this is a very uncertain mode, as different gems have not unfrequently the same colour; and, in many cases, the same gems are of different colours. The usual distinction of gems into Oriental and Occidental is also liable to error, as the best gems, from whatever part of the world they are brought, are always called Oriental. The most estimable of all the kinds are the diamond ([50]), ruby ([54]), emerald ([67]), and sapphire ([53]); and stones a grain in weight, and equal in quality, are valued in the following proportions, at 8l. per carat for diamonds, 4l. for rubies, and 3l. for each of the others. The amethyst ([79]), topaz ([61]), and aqua-marine ([61]), are considered of nearly equal value with each other; and the garnet ([70]) is the cheapest of precious stones.

The ancients engraved upon several kinds of gems; but they appear to have been ignorant of the art of cutting the diamond, the ruby, and the sapphire, which were too hard for them to operate upon. The emerald and the noble opal ([102]) were too highly esteemed as precious stones to have often found their way into the hands of engravers. It has been asserted that the ancients did not use the topaz for engraving; but there is extant a beautiful intaglio, representing an Indian Bacchus, which is said to be a topaz. The garnet was often engraved upon: and there are many master-pieces of the art in calcedony ([91]) and carnelian (93.) Onyx and sardonyx ([92]) were employed for that species of engraving in relief called cameos; and, in many instances, it is pleasing to observe with what dexterity the ancient artists availed themselves of the different colours in the alternate zones to express the different parts and shades of their figures.

Most of the gems may be imitated by artificial preparations of glass, coloured by different metallic substances; and it is not easy, by mere inspection, to distinguish the better kinds of factitious stones from real gems. They are, however, discoverable by a deficiency of lustre, and being so soft as, even in the most perfect kinds, to yield to the point of a steel instrument.

The cutting and polishing of gems is the work of the lapidary, and is in general thus performed:—The shape most proper to be given to any particular gem being determined on, the stone is cemented to the end of a stick, and the different facets are formed by a mill contrived for the purpose. This mill is a plate of copper, or an alloy of lead and tin, to which an horizontal motion is given by very simple machinery, and the surface of which is charged either with diamond powder and oil, or with fine emery and water. A thick peg of wood called a gauge, pierced with small holes in all directions, is set upright on the lapidary’s bench, close to the mill, and the process of shaping the facets thus takes place. The stone is placed on the surface of the mill, the opposite end of the stick to which it is cemented being inserted in one of the holes of the gauge. In this position it is kept steady by the workman, with his right hand, whilst, with the other, he puts the mill in motion. The skill of the lapidary depends on regulating the velocity of the mill, and pressing with more or less force on the stick, with an almost imperceptible tendency to one or other direction in different stages of the work, examining each facet at very short intervals, in order to give as great precision as possible to its size and form. This part of the business being completed, the cutting mill is taken out, and replaced by one of brass, on which the polishing is performed by means of fine emery ([58]), tripoli, and rotten stone ([119]), exactly in the same manner as is practised in the first stage of the process for setting the facets.

DIAMOND.

50. The DIAMOND, or ADAMANT of the ancients, is the most valuable of gems, and the hardest of all known bodies; when pure, it is perfectly transparent.

In a rough state, diamonds have usually either the form of rounded pebbles, with a shining surface, or they are crystallized in the shape of octohedrons, or double four-sided pyramids. ([Pl. II, Fig. 5, 6].) Though for the most part colourless, they are sometimes yellow, green, blue, blackish, or rose-coloured.

The best diamonds are brought from the East Indies. The principal mines are those of Raolconda and Coulour, in the province of Golconda; and that of Soumelpour, or Goual, in Bengal. At Raolconda they are found in the deep crevices of rocks. Persons, by means of long iron rods, with hooks at the end, draw out from these crevices the loose contents, and afterwards wash them in tubs, for the purpose of discovering the diamonds.

The first discovery of diamonds at Coulour was about two centuries ago, by a countryman, who, on digging his ground to sow millet, accidentally found one of these stones of large size. From that period the whole adjacent plain began to be searched to the depth of from ten to fourteen feet; and the work was, at one time, so extensively pursued, that nearly 6,000 persons were employed in it. At Soumelpour the diamonds are found amongst the sand and gravel of the river.

Diamonds are likewise found in the island of Borneo, and in several parts of South America. The mode by which they are obtained from one of the rivers of Brazil has been described by Mr. Mawe. The current is turned, and part of the bed of the river being laid dry, the mud is taken up and washed, by negroes, in places prepared for the purpose, through which a portion only of the stream is allowed to flow. As soon as all the earthy particles have been washed away, the gravel-like matter that remains is raked together, the stones are thrown out, and what diamonds happen to be present are found amongst the refuse that is left.

To ascertain whether a stone, that has been found, be really a diamond, the workmen have a mode of placing it upon a hard substance, and striking it with a hammer. If it either resists the blow or separate into leaves, it must be a diamond; but, in the latter case, the discovery is sometimes made at an immense expense, as, by thus diminishing the size, its value must also, of course, be greatly diminished.

Diamonds are generally exported from Madras in a rough state; and in small parcels neatly sewed in muslin, and sealed by the merchants who send them. These, we are informed by Mr. Milburne in his valuable work on oriental commerce, are, for the most part, sold in Europe by the invoice, as it is called; that is, without being opened: and he says that they are always found to contain the value for which they were sold in India.

Of all transparent substances, none for brilliancy can be compared with the diamond. Its hardness is such, that no steel instrument whatever can make any impression upon it. Notwithstanding this, at a temperature not so high as that which is required for the melting of silver, it gradually dissipates and burns. Diamonds have been shown to consist principally of carbon or charcoal in a pure and crystallized state.

The ancients, ignorant of the art of cutting diamonds, were contented to set them in a native state; and for this purpose they preferred such stones as had naturally a crystallized form. The four large diamonds which ornament the clasp of the Imperial mantle of Charlemagne, and which are still preserved in Paris, are uncut stones of this description. The extreme hardness of the diamond baffled all attempts to polish it in such manner as to exhibit its peculiar beauty, until the year 1456, when a young man of Bruges, whose name was Berquin, endeavoured to polish two diamonds by rubbing them against each other. Having succeeded in this, he next constructed a wheel, on which, by means of diamond powder, he was enabled to cut and polish these gems in a manner beyond his greatest expectation. Since this period the art of polishing them has been greatly improved both by the Dutch and British jewellers.

In the choosing and valuing of diamonds in a rough state, attention is paid to their colour, their being free from extraneous matter, and their shape. Those that are most perfect are crystalline, and resemble a drop of clear spring water, in the middle of which is to be perceived a strong light, that plays with great spirit on moving them about. When they have a yellowish or greenish tinge they are considered to be bad. Many diamonds have a kind of confused structure, which lapidaries compare to knots formed in wood. These are rejected, from the impossibility of polishing them properly.

Mr. Mawe remarks that diamonds, when rubbed together, have a peculiarly and scarcely to be described grating sound, which is one of their most remarkable characteristics. By this alone rough diamonds may be accurately and expeditiously distinguished from every other gem.

It is usual to cut diamonds into three principal forms, called brilliant ([Pl. II, Fig. 7]), rose ([Fig. 8]), and table diamonds ([Fig. 9]). Brilliants are, for the most part, cut from such of the stones as have naturally a crystallized shape, and rose diamonds from the flat varieties. The former are so called from their great lustre, in consequence of the facets on both sides being cut. These are always set upon a black ground, whilst rose diamonds, which are much thinner, are set upon a white foil speckled with black, for the purpose of adding to their lustre. Rose-cut diamonds are of course much less estimable than brilliants; so much so indeed, that of late many of them, brought from Holland, have been re-cut into brilliants, notwithstanding the additional expense, and the loss of size necessarily attendant on this operation. The table diamond is the least beautiful of any. This mode of cutting is only adopted for such stones, or rather fragments, as, with a considerable breadth, have only a very trifling depth. The diamond-cutters of England are considered to be the best in Europe, but their number is so small as to occasion many stones to be sent to Holland to be cut.

The value of diamonds is ascertained by their weight in carats; and this value increases, in a very high ratio, according to their magnitude. For instance, a diamond weighing one carat will be worth about 10l. whilst another of five carats will be worth 150l. and of ten carats 800l.[^[2]] This rule, however, can only be taken for diamonds of twenty carats and under. The larger ones, in consequence of the scarcity of purchasers, are generally disposed of at prices greatly inferior to their estimated worth. The value of some diamonds that are peculiarly perfect exceeds the above ratio; whilst, for a stone that is cloudy, foul, or of bad colour, even three quarters of the estimated value will perhaps be deducted.

[2]. A Carat is equal to four jeweller’s grains, seven grains of which are equal to six grains troy. To ascertain the value of wrought diamonds the weight must be doubled, about half being supposed to be lost in the working. This sum must be multiplied into itself, and the product by two. Thus to find the value of a diamond of twenty carats 20 × 2 = 40 × 40 = 1600 × 2 = 3,200l.

No diamonds are so valuable as those that are perfectly transparent, and of snow-white colour. The green and yellow varieties are, however, much esteemed: the blue kinds were formerly more valued than at present; and the least valuable are those that have a grey or brownish tint. Black diamonds are much prized by collectors.

The principal use of the diamond is in jewellery. It is also used by lapidaries, for slitting hard stones, and for cutting and engraving upon other gems; by clock-makers in the finer kinds of clock-work; in the glass-trade for squaring large pieces or plates of glass, and among glaziers for cutting their glass.

The largest diamond ever known (if it be such, and not a white topaz, as some people have imagined) is in the possession of the Queen of Portugal, and weighs 1,680 carats, or more than eleven ounces. It was found in Brazil, and sent to Lisbon in the year 1746. It is still uncut, and has been valued at 5,644,800l.

The Rajah of Mattan, in the island of Borneo, possesses a large diamond, shaped like an egg, with an indented hollow near the smaller end. It was found in that island about eighty years ago, is said to be of the finest water, and to weigh 367 carats, or more than two ounces and a quarter. Several years ago the Governor of Batavia, desirous of purchasing this gem, sent a Mr. Stuvart to the Rajah, authorizing him to offer for it 150,000 dollars, two large brigs of war, with their guns and ammunition, together with a certain number of great guns, and a quantity of powder and shot. The Rajah, however, refused to deprive his family of so valuable an hereditary possession; for the Malays not only attach to it the miraculous power of curing all diseases by means of water in which it is dipped, but also believe that the fortune of the family is sustained by its continuing in their possession.

Tavernier, the French Traveller, saw in the possession of the Great Mogul a diamond which weighed near 280 carats. In form and size it resembled half a hen’s egg. This diamond had been obtained from the mine of Coulour, about the year 1550; and was valued at more than 700,000l. sterling.

The sceptre of the Emperor of Russia is adorned with an oriental diamond about the size of a pigeon’s egg, which weighs 195 carats. This diamond is said to have once been placed as the eye of an idol in Seringham, in the Carnatic. A grenadier, who had deserted from the French service in India, contrived to become one of the priests of the idol, in the hope of being able to steal this eye. He at length effected his purpose, and escaped with the diamond to Madras, where he sold it to the captain of a ship for a sum equal to 2,500l. of British money. It was afterwards transferred to a Jew for 18,000l. Coming into the hands of a Greek merchant, he offered it for sale at Amsterdam, in 1766; and the Russian Prince Orloff bought it for the Empress Catharine for about 90,000l. sterling, and an annuity of 4,000l. during the life of the person who sold it.

The Pitt, or Regent diamond ([Pl. II, Fig. 10]), which lately was set in the handle of the sword of state of Buonaparte, and is now possessed by the king of France, is a brilliant of the most beautiful kind, and weighs 136¾ carats. It was brought from India by Thomas Pitt, Esq. Governor of Fort George. Mr. Pitt has himself stated, respecting it, that, in December, 1701, whilst resident in Madras, several valuable stones, in a rough state, were brought to him for sale by an eminent diamond merchant. One of these, the diamond here spoken of, was so large that the merchant asked for it the sum of 85,000l. After much bargaining, Mr. Pitt purchased it for 20,400l. He afterwards sold it for 135,000l. to the Regent Duke of Orleans; and by him it was placed among the crown jewels of France.

The Pigot diamond weighs forty-seven and a half carats. This, which is an extremely fine stone, was disposed of by lottery, in 1800, for 22,000l.; and is now in the possession of Messrs. Rundell and Bridge, jewellers in London.

A large star, cross, and chain, worn on grand gala days by the Prince of Brazil, as Sovereign of the different Portuguese orders of knighthood, are each ornamented with a great number of magnificent diamonds, set in gold. The centre diamond of the star is alone valued at 800,000l.

When the diamond is rubbed it will attract bits of straw, feathers, hairs, and other small objects; and if exposed to the rays of the sun, and immediately taken into a dark place, some diamonds will appear luminous.

ZIRCON FAMILY.

51. JARGOON is a gem usually of smoky yellow or brownish colour, and sometimes limpid: if placed upon any object, it exhibits of it a very distinct double image.

The primitive form of its crystal is an octohedron ([Pl. II, Fig. 5]), but it is frequently crystallized in right-angled prisms, terminated by four-sided pyramids.

In hardness this stone does not much exceed that of the emerald. The greyish white and yellowish white varieties of jargoon are valuable chiefly on account of their resemblance to the diamond. The darker-coloured varieties can be deprived of their colour by heat; and, in this state, though in lustre they are infinitely inferior to them, they are sometimes substituted for diamonds. Jargoons are now seldom used except for the jewelling of watches and time-pieces. About a century ago, they were much used in mourning ornaments, for which the dark tone of their colour, and their almost adamantine lustre, were supposed to be peculiarly appropriate.

The jargoon is principally brought from the island of Ceylon; but it is occasionally found in France, and Spain, and in granite rocks near Cuffel, in Dumfrieshire, Scotland.

52. The Hyacinth, or Jacinth, is a dark orange-red variety of jargoon. It is also chiefly imported from Ceylon, where it is generally found in the sand of rivers, in irregularly round pieces, but seldom of large size without flaws.

This stone is indebted for its name to a supposed resemblance in colour to that flower, which, according to the Pagan mythology, Apollo raised from the blood of his favourite youth, Hyacinthus.

When bright, and free from flaws, the hyacinth is a superb ring stone; but it is not of usual occurrence in modern jewellery.

RUBY FAMILY.

53. The ORIENTAL SAPPHIRE is a gem of blue colour, the shades of which vary from a full and deep tint to a nearly colourless appearance, and sometimes it is party-coloured.

It is found crystallized in six-sided pyramids much lengthened and joined base to base ([Pl. II, Fig. 13]); and also in rounded or pebble-shaped fragments. It has a foliated texture, is extremely hard, and about four times as heavy as water.

We are chiefly indebted for the sapphire to the East Indies and the Island of Ceylon, where it is found amongst the sand of the rivers. When brought into Europe, it is cut by means of diamond powder, and polished with emery. It is now usually set with a foil of its own colour; but it was formerly the practice, instead of foil, to place under this stone the blue part of a peacock’s feather.

In hardness the sapphire ranks next to the ruby ([54]); and in value it is about equal to the emerald ([67]). A good sapphire of ten carats’ weight is worth about fifty guineas. In the Museum of Natural History at Paris there is a sapphire which weighs upwards of sixty-six carats: it was placed there from the wardrobe of the crown.

We are informed by M. Hauy that sapphires are found in Bohemia and France, particularly in one part of the Ville du Puy, among the sand of a rivulet near Expailly. In the summer-time, when the rivulet is nearly dry, they are collected by persons, each of whom is furnished with a small tray and a linen bag. Where-ever there are small depressions in which the water has been stationary, these persons enter them, and fill their trays with the sand. This they wash in water in such manner that the lighter particles are carried away; whilst the heavier ones of gravel, sapphire, and other articles, remain at the bottom.

Some sapphires exhibit a kind of opalescence, or whitish floating light in their interior. Sapphires lose all their colour in the fire; and, after having been subjected to heat, they are so hard and transparent as sometimes to be sold for diamonds.

54. ORIENTAL RUBY is a precious stone of intense and bright red colour, occasionally varied with blue, and sometimes party-coloured.

In the general form of its crystals it much resembles the sapphire ([53]).

The ruby is imported into this country from the East Indies, though seldom in a rough state, as the stones are almost always first cut by the Indians for the purpose of ascertaining their value. They are said to be found in the sand of certain streams near the town of Sirian, the capital of Pegu; and with sapphires in the sand of rivers in Ceylon. But they are so seldom seen of large size, that a ruby above thirty-one carats’ weight, of perfect colour, and without flaws, is even more estimable than a diamond of equal weight. The ruby is usually set with a foil; but, if peculiarly fine, it is sometimes set without bottom, that the stone may be seen through.

Tavernier, the Eastern traveller, states that, in the throne of the Great Mogul, he saw 108 rubies, which, on an average, weighed from 100 to 200 carats each. Among the jewels of the King of Candy, that were sold by auction in London, on the 13th of June, 1820, was a ruby which measured two inches in length, and one inch in breadth. It was, however, interesting only as a specimen for a cabinet, for it had, in various directions, a great number of small hair-like tubes running through it.

The hardness of this stone is such that the ancients do not appear to have possessed the art of cutting it; and, in the improvements which of late have been made by Mr. Earnshaw in the construction of time-keepers, no stones have been found sufficiently hard for jewelling the holes, except the ruby and the diamond.

There are several modes of counterfeiting rubies; and some persons have succeeded so well in imitating these stones, that even the most able lapidaries, till they try the hardness, may be deceived.

55. The Oriental Amethyst is an extremely rare gem, usually of purple colour, apparently formed by an union of the colouring matter of the sapphire and the ruby. This stone, if heated, loses its colour, and becomes transparent. After this process its brilliancy is such that it is scarcely distinguishable from the diamond; and, in jeweller’s work, it is occasionally substituted for that gem. The common amethyst ([79]), or that which is chiefly seen, is nothing more than a violet-coloured rock crystal ([78]).

56. The Oriental Topaz and Emerald are each varieties of the oriental ruby, the former straw-coloured and the latter green. This kind of emerald is imported from Pegu, and some other parts of the East Indies, and is an extremely rare gem.

57. The SPINEL and BALAIS RUBY are two kinds of precious stones, which differ from each other principally in colour, the former being of a carmine, and the latter a cochineal red.

They vary from the oriental ruby ([54]) in being less hard; in the primitive form of their crystals being regular octohedrons ([Pl. II, Fig. 5]), and in their not being much more than 3 times heavier than water.

Although these two kinds of rubies are inferior, both in lustre and colour, to the oriental ruby; yet, when they exceed a certain size, they are much esteemed. A spinel that weighs more than four carats is valued at half as much as a diamond of the same weight, and is not unfrequently imposed upon ignorant purchasers for the oriental species. It is easily wrought, takes a high polish, and is certainly a beautiful gem. Being too expensive for necklaces, it is usually set in rings and brooches, surrounded by brilliants.

The spinel ruby is found amongst sand, in one of the rivers of Ceylon, which flows from the high mountains, towards the middle of the island. It is also found in Brazil; and in Hungary, Bohemia, and Silesia.

The Balais ruby is so named from Balacchan, the Indian appellation of Pegu, from which country it is chiefly imported.

58. EMERY is a very hard opaque mineral, of blackish or bluish grey colour, which is chiefly found in shapeless masses, and mixed with other minerals. It is about four times as heavy as water.

The best emery is brought from the Levant, and chiefly from Naxos, and other islands of the Grecian Archipelago, where it occurs abundantly, in large, loose masses, at the foot of primitive mountains. It is also found in some parts of Spain; and is obtained from a few of the iron mines in our own country.

In hardness it is nearly equal to adamantine spar; and this property has rendered it an object of great request in various arts. It is employed by lapidaries in the cutting and polishing of precious stones; by opticians, in smoothing the surface of the finer kinds of glass, preparatory to their being polished; by cutlers, and other manufacturers of iron and steel instruments; by masons, in the polishing of marble: and, in their respective businesses, by locksmiths, glaziers, and numerous other artisans.

For all these purposes it is pulverized in large iron mortars, or in steel mills; and is afterwards separated, according to the several degrees of fineness that are required, by washing it in water, and suffering the grosser particles to deposit themselves. By this operation the finer particles, which remain suspended in the water, and which are obtained by decanting the water off, and suffering it to stand for a considerable time, are separated. The particles first deposited are again ground, and again agitated in the water, to separate the finest. By these successive operations the emery is reduced to a powder so fine that, when rubbed between the fingers, it communicates no sensation whatever of grittiness. In general those particles only of the emery which remain suspended in the water, after it has stood about half an hour, are used to polish metals.

59. ADAMANTINE SPAR, or IMPERFECT CORUNDUM, is a very hard and nearly opaque stone, which varies much in colour, but is chiefly grey, with a greenish, brown, or bluish tint.

It is usually found in the form of six-sided prisms, but it sometimes occurs in shapeless masses, has a foliated texture, and is about four times as heavy as water.

The name of adamantine spar was given, by the British lapidaries, to this substance from its hardness being nearly equal to that of the diamond. It was originally discovered among the granite rocks of China; but it has since been found, and in greater purity, in Bengal and Ceylon.

In a powdered state this substance has long been used by the artists of India and China for the cutting and polishing of precious stones, and even of the diamond; but, though it will in some degree operate upon that gem, it is not sufficiently hard to bring out the peculiar beauty of it in a degree at all comparable to that which is effected by the European lapidaries with diamond powder. The Chinese also use adamantine spar for polishing steel, and in the composition of the finer kinds of porcelain or earthenware. For the cutting of seals and precious stones European workmen consider it preferable to emery; but, for minute engraving, it is much inferior to diamond powder.

60. CHRYSOBERYL is a gem of yellowish or brownish green colour, harder than quartz ([76]), and sometimes transparent; but often only semi-transparent, in which case it exhibits a bluish light, floating in the interior of the stone.

It is usually found in rounded pieces, but is sometimes crystallized in compressed six-sided prisms, and in double six-sided pyramids.

So little is this gem in request in Europe, that it is seldom to be found in the possession of jewellers; but in Brazil it is considered inferior only to the diamond. It is usually procured from South America; yet it occurs in Saxony; and, with the ruby and sapphire, amongst sand in the rivers of Ceylon.

Such is the hardness of the chrysoberyl, that, when properly polished, which is a difficult operation, it is capable of receiving a lustre nearly equal to that of the diamond. We are informed that, a few years ago, a considerable number of these gems were imported into this country from Brazil, but that the greater part of them were entirely spoiled by inferior workmen, and that the rest were so ill-cut that they remained unnoticed, and without value. The smaller stones are said to appear to most advantage in circular ear-drops; and the larger specimens form necklaces and ring stones of great beauty.

The variety which exhibits an opalescent appearance, or presents a bluish light, undulating as it were in the interior of the stone, and changing its situation according to the position of the observer, is chiefly valuable as an article of curiosity: the transparent kind is always preferred by the jeweller.

SCHORL FAMILY.

61. The TOPAZ is a gem usually of a wine-yellow colour, but sometimes orange, pink, blue, and even colourless, like rock crystal; of a lamellar or foliated structure, harder than quartz, but not so hard as ruby.

It varies considerably in its crystallization; is 3½ times heavier than water; and, when placed upon any object, shows a double image of it.

The name of topaz is derived from an island in the Red Sea, where the ancients found a stone, but very different from ours, which they denominated topaz. The best topazes are of a deep colour, and are imported from Brazil; the most brilliant ones are supposed to be those of Saxony; but the latter are generally of very pale colour. This species of gem is found in many parts of Europe, but defective in transparency, and sometimes even opaque. It occurs in large crystals, and rolled masses, in an alluvial soil ([269]), in the upper parts of Aberdeenshire, Scotland; and in veins, along with tin-stone, at St. Anne’s, in Cornwall. Topazes, more than a pound in weight, have been found in Scotland.

Mr. Mawe speaks of a topaz mine at Capon, near Villa Rica, in Brazil. In two breaks or slips of the rocks, he says, there were little soft places where the negroes found the topazes by scraping in them with pieces of iron. He himself observed at least a cart-load of inferior topazes, any number of which he might have taken away; but all that he saw were defective and full of flaws.

These stones vary much in size; some, particularly those of Siberia, being extremely small, and others being upwards of an inch in thickness. In the Collection of Natural History at Paris there is a Brazilian topaz which weighs four ounces and a quarter. These stones are not sufficiently scarce to be, in general, much valued by the jeweller or lapidary. The deep yellow variety is preferred to the pale sort, although the latter is often superior to it both in size and hardness.

Figures have sometimes been engraved on the topaz; and these, when well executed, are of great value. In the National Museum at Paris there is a superb Indian Bacchus engraven on a topaz. The cabinet of the Emperor of Russia contains several fine topazes of this description.

Some of the coarse kinds of topaz are broken down, pounded, and used instead of emery for the cutting of hard minerals; and powdered topaz was formerly kept in apothecaries’ shops, and sold as an antidote against madness.

It is a somewhat singular circumstance, that, if the Saxon topaz be gradually exposed to a strong heat in a crucible, it will become white and, on the contrary, that Brazilian topazes by the same process become red or pink. By exposure to a still stronger heat, the Brazilian topaz changes its colour to a violet-blue.

Jewellers usually divide topazes into the following kinds:

62. Brazilian and Saxon, already mentioned.

63. Bohemian.—These are found chiefly in the tin mines of Bohemia, are of small size, deficient in transparency, have only grey or muddy white colours, and are of little value.

64. Blue Topaz.—This is a large Brazilian gem, which varies in size from one or two carats to two or three ounces. A fine blue topaz, without flaw, and which weighed an ounce and a quarter, was sold for 200 guineas. It is sometimes difficult to distinguish a blue topaz from an aqua marine ([68]).

65. Pink Topaz.—Some beautiful rose-coloured varieties of topaz have been brought from Asia Minor, and others are found in South America; but the pink topazes in the jewellers’ shops are chiefly stones of the yellow Brazilian kind, which have had their colour changed by heat.

66. The White, or Nova Mina Topaz, is a perfectly colourless and transparent variety. It generally occurs of small size, and is in considerable estimation in Brazil for ear-rings, or for being set round yellow topazes. Small stones of this description have recently been found at St. Michael’s Mount, in Cornwall.

There is imported from Brazil a yellow kind of crystal ([83]), which is so similar, in its appearance, to the yellow topaz as sometimes to be imposed upon purchasers for that stone.

67. The EMERALD is a well-known gem, of pure green colour, and somewhat harder than quartz.

Its natural form is a short six-sided prism; but it is sometimes found massive, and rounded like a pebble.

By the ancients the emerald was a gem much in request, and particularly for engraving upon. They denominated it smaragdus, and are said to have procured it from Ethiopia and Egypt; but, besides the true emerald, Pliny, under this title, includes green jasper ([96]), malachite ([231]), fluor spar ([194]), and some other green minerals. The pillars of emerald in the temple of Hercules at Tyre, mentioned by Herodotus, and the large emeralds described by Pliny as having been cut into columns and statues, cannot be referred to the true emerald.

The deepest coloured and most valuable emeralds that we are acquainted with are brought from Peru. They are found in clefts and veins of granite, and other primitive rocks; sometimes grouped with the crystals of quartz ([76]), felspar ([110]), and mica ([123]); and, not unfrequently, loose in the sand of rivers. The most ancient emerald mine is that of Manta, in Peru, but it has been some time exhausted; and most of the emeralds that are now brought to Europe are obtained from a mine situated in the valley of Tunca, between the mountains of New Grenada and Popayan.

The emerald is one of the softest of the precious stones; and is almost exclusively indebted for its value to its charming colour. The brilliant purple of the ruby, the golden yellow of the topaz, the celestial blue of the sapphire, are all pleasing tints; but the green of the emerald is so lovely, that the eye, after glancing over all the others, finds delight in resting upon this. In value it is rated next to the ruby; and, when of good colour, is set without foil and upon a black ground, like a brilliant diamond. Emeralds of inferior lustre are generally set upon a green gold foil. These gems appear to greatest advantage when table cut ([Pl. II, Fig. 9]), and surrounded by brilliants, the lustre of which forms an agreeable contrast with the quiet hue of the emerald. They are sometimes formed into pear-shaped ear-drops; but the most valuable stones are generally set in rings. A favourite mode of setting emeralds among the opulent inhabitants of South America is to make them up into clusters of artificial flowers on gold stems.

The largest emerald that has been mentioned is one said to have been possessed by the inhabitants of the valley of Manta, in Peru, at the time when the Spaniards first arrived there. It is recorded to have been as big as an ostrich’s egg, and to have been worshipped by the Peruvians, under the name of the Goddess, or Mother of Emeralds. They brought smaller ones as offerings to it, which the priests distinguished by the appellation of daughters. Many fine emeralds are stated to have formerly been bequeathed to different monasteries on the Continent; but most of them are said to have been sold by the monks, and to have had their place supplied by coloured glass imitations. These stones are seldom seen of large size, and at the same time entirely free from flaws.

The emerald, if heated to a certain degree, assumes a blue colour; but it recovers its proper tint when cold. When the heat is carried much beyond this, it melts into an opaque coloured mass.

The precious stone called oriental emerald ([56]) is a green and very scarce variety of the oriental ruby.

68. The BERYL, or AQUA MARINE, is a light or mountain green variety of the emerald, sometimes straw-coloured, bluish, yellow, or even white.

These stones are of such frequent occurrence, even in large pieces perfectly clear and free from flaws, they are in general so soft, and have so little the brilliancy of other gems, that they are usually considered of inferior value. The most beautiful kinds are brought from Dauria, on the frontiers of China, from Siberia, and from Brazil. They are also found in Saxony and the South of France, and are very common at Baltimore, in North America. Specimens of aqua marine have been obtained from the upper parts of Aberdeenshire, Scotland, where they sometimes occur in alluvial soil, along with rock crystal and topaz. These stones have also been found, embedded in granite, near Lough Bray, and Cronebane, in the County of Wicklow, Ireland; and also in mountain rock, in some parts of Devonshire.

They are cut by means of emery ([58]), and polished with tripoli ([119]). The darkest green specimens are set upon a somewhat steel-coloured foil; and the pale ones are either placed, like the diamond, on a black ground, or upon a silvery foil. The aqua marine is usually made into necklaces; but it is likewise employed for brooches, and not unfrequently for steel stones and intaglios. The larger ones are in much esteem among the Turks for the handles of stilettos.

69. The TOURMALINE is a stone belonging to the same family as the emerald, and generally of a smoky blackish colour: sometimes, however, it is green, red, blue, or brown; and, when not very thick, it is transparent.

It is occasionally found in shapeless masses, but more frequently crystallized in three, six, or nine-sided prisms, variously truncated or terminated; and its weight is somewhat more than three times that of water.

This stone was first made known in Europe, about the beginning of the last century, by the Dutch merchants, who brought it from the island of Ceylon, where it is principally found. When strongly heated it becomes electric; one of the summits of the crystal negatively, and the other positively. An early writer, by whom it is mentioned, says, that “it has the property not only of attracting ashes from the warm or burning coals, but that it also repels them again, which is very amusing: for as soon as a small quantity of ashes leaps upon it, and appears as if endeavouring to writhe themselves by force into the stone, they in a little time spring from it again, as if about to make a new attempt. It was on this account that the Dutch called it the ashes drawer.”

Since the above period, tourmaline has been found in Brazil; and in Norway, Germany, France, and several other parts of Europe. It generally occurs embedded in different kinds of mountain rock; and, in these, is rather confined to single beds or strata, than disseminated through the whole mass of the mountain. A piece of tourmaline, of cylindrical form, and brownish grey colour, was some time ago discovered in the neighbourhood of Kitt-hill, near Callington, Cornwall. Black tourmaline, both in large and small crystals, is found in granite rock, in the vicinity of the Logan, or Rocking-stones, near Treryn, in the same county.

When laid on a table, the tourmaline appears a dark and opaque stone; but, when held against the light, it has generally a pale brownish hue. It is sometimes cut, polished, and worn as a gem; but, on account of the muddiness of its colours, it is not in general much esteemed. Those persons who wear tourmalines set in rings consider them more as objects of curiosity than of elegance: they show them as small electrical instruments, which, after being heated a little while by the fire, will attract and repel light bodies.

In the superb collection of minerals of the British Museum, there is a magnificent specimen of red tourmaline, or rubellite, which has been valued at 1000l. sterling. It was presented by the King of Ava to the late Colonel Symes, when on an embassy to that country, and was afterwards deposited by the latter in Mr. Greville’s collection; with that collection it became the property of the British Museum.

GARNET FAMILY.

70. The PRECIOUS, or NOBLE GARNET, is a gem of crimson colour, which, when crystallized, has the form of a twelve-sided solid ([Pl II, Fig. 11, 12]). It is sufficiently hard to scratch quartz, and is about four times as heavy as water.

This stone is found abundantly in many mountains (particularly of primitive rock), in different parts of the world. But garnets of the hardest and best quality are brought from Bohemia, where there are regular mines of them; and a great number of persons are there employed in collecting, cutting, and boring them. The boring is performed by an instrument having a diamond at its extremity, which is rapidly turned by a bow. The work is so expeditiously performed, that an expert artist can bore 150 garnets, or he can cut and polish thirty, in a day. In Suabia there are two towns in which upwards of 140 persons are employed in these operations.

In general garnets are stones of inferior value. When compared with the ruby, those even of finest quality have a very sombre appearance. The kinds most esteemed are such as have a clear and intense red colour, or a rich violet or purplish tinge. The best garnets are cut in the manner of other precious stones, and are usually set upon a foil of the same colour. To heighten the colour and transparency of certain garnets, jewellers either form them into what are called doublets, by attaching to the lower part of the stone a thin plate of silver, or they hollow them underneath.

Crystals of garnet sometimes occur three or four inches in diameter. These are cut into small vases; which, if of good colour, and free from defects, are highly valued. Many fine engravings have been executed on garnet. One of the most beautiful that is known is a figure of the dog Sirius, in the possession of Lord Duncannon.

The coarser kinds of garnet are used as emery for the polishing of other minerals; and are thus prepared. They are made red-hot, then quenched in water, reduced to powder in an iron mortar, and lastly diffused through water, poured into other vessels, and allowed to settle, in order to obtain an uniform powder. This powder is known to artists by the name of red emery.

It has been conjectured that our garnet was the same kind of stone which, on account of its colour, the ancients denominated carbuncle.

71. Common Garnet.—A very inferior variety of garnet, of brown or greenish brown colour, is found in our own country, and particularly amongst rocks near Huntley, in Aberdeenshire, Scotland. These garnets, however, are, in general, so soft as to be of little value to the lapidary; and consequently are seldom cut or polished for ornamental purposes. But being easily fused, and abounding in iron, they are occasionally employed as a flux in the smelting of rich iron ores: and as an addition to poor ones.

72. Syrian Garnets are distinguished by their violet or purplish tinge. Some writers state that they have their name from the word Soranus, which signifies a red stone; and others from Sirian, a town in Pegu, where they are said to be found in great beauty.

73. Pyrop Garnets are of a dark blood-red colour, which, when the stones are held between the eye and the light, falls strongly into yellow: they are chiefly brought from Bohemia: are employed in almost every kind of jewellery, and generally set with a gold foil. At Waldkirch, in Suabia, there are twenty-four mills for the cutting and polishing of pyrop garnets: and 140 masters are occupied in manufacturing these stones.

74. Vesuvian is a liver-brown kind of garnet, that was originally found among rocks ejected from Mount Vesuvius; and in the vicinity of which mountain it still occurs in considerable abundance. At Naples it is cut into stones for rings and other ornaments. Vesuvian has of late years been found in other parts of Europe; and even at Kilranelagh, and Donegal, in Ireland.

75. Cinnamon Stone is a kind of garnet of hyacinth-red colour, which is found in angular and roundish pieces among the sand of rivers in the island of Ceylon. It is cut as a precious stone; and, when of good colour, and free from flaws, is of considerable value.

QUARTZ FAMILY.

76. COMMON QUARTZ is a hard and foliated substance, usually of white or grey colour, and more or less transparent.

It is generally found in shapeless masses, which are nearly thrice as heavy as water, and the fracture of which is glassy. When crystallized, it most commonly has the form of a six-sided prism, terminated by a pyramid of six sides.

This kind of stone forms a constituent part of many mountains, and is very common in our own, as well as in most other countries. It is sufficiently hard to scratch iron and steel; and it has the property, after having been several times successively made red-hot, and dipped into water, of communicating to that fluid a certain degree of acidity.

Quartz is employed, in place of sand, for making the finer kinds of glass; and also in the manufacture of porcelain. For the latter purpose great quantities are collected from the mountains of Wales, ground into powder, and in that state shipped to Liverpool, and other parts. After having been burnt and reduced to powder, it is sometimes mixed with clay, and formed into bricks for the construction of glass furnaces: these are capable of resisting the intense heat which is requisite in the fusion of glass.

77. Burrstone is a vesicular and corroded variety of quartz, which forms a most excellent and valuable kind of millstone. It is chiefly found in France; but is so much esteemed by the English millers, that the Society of Arts, in London, for many successive years, offered a considerable reward for its discovery in Great Britain. At length a vein of burrstone was discovered in the Moel y Golfa hills, North Wales, by a Mr. Evans, who, in consequence received a premium from the Society. About the same time another vein was opened near Conway; and the same Society, in 1800, gave a premium of 100l. to the widow and orphan children of the discoverer. Both these quarries were sufficiently convenient for water carriage; yet the demand for the Cambrian burr did not answer the expectation, and millstones of French production were still preferred to them.

The mode of splitting these stones, as it is practised in some parts of France, is singular, and affords a proof of the extraordinary power of capillary attraction. The blocks are first cut into the form of cylinders, sometimes many feet in height. To split these horizontally into millstones, circular indentations are made round them, at proper distances, according to the thickness that is to be given to the stones; wedges of willow, that have been dried in an oven, are then driven into the indentations with a mallet. When these have been sunk to a proper depth, they are moistened with water; and, after a few hours, the several stones that have been marked out are found to be perfectly separated.

78. ROCK CRYSTAL is an extremely beautiful kind of quartz, sometimes perfectly transparent, and sometimes shaded with grey, yellow, green, brown, or red. It occurs in the form of crystals with six sides, each terminated by a six-sided prism.

The name of this substance was considered by the ancients to signify ice, or water crystallized; and they imagined that crystal was produced from a congelation of water.

Its uses are numerous. It is cut into vases, lustres, and snuff-boxes; and many kinds of toys of extremely beautiful appearance are made of it. When pure and perfectly transparent, it is much in request by opticians, who make of it those glasses for spectacles which are called pebbles, and who use it for various kinds of optical instruments. The best crystal is imported from Brazil and Madagascar, in blocks, not unfrequently from fifty to a hundred pounds in weight.

This stone is wrought into the different shapes that are required, by sawing, splitting, and grinding. The sawing is effected by an extended copper wire fixed to a bow: the wire is coated with a mixture of oil and emery, and is drawn backward and forward until the operation is performed. But, as this process is a tedious one, particularly when the mass is large, a more expeditious, although less certain, method is sometimes adopted. The crystal is heated red hot, and a wet cord is drawn across, in the direction that the workman intends to split it. By the rapid cooling thus effected, in the direction of the cord, the stone easily splits by a single blow of the hammer, and generally in the direction required. The grinding is performed by means of emery: and the polishing effected by tin ashes and tripoli.

The ancients held vases that were made of this stone in great estimation, particularly when they were of large size. Of two cups which the tyrant Nero broke into pieces in a fit of despair, when informed of the revolt that caused his destruction, one was estimated to be worth more than 600l. of our money. The most valuable kind of crystal that was known to the ancients was obtained from the island of Cyprus; but it was often faulty in particular parts, having flaws, cracks, and blemishes. When the crystal was used for the engraving of intaglios and cameos, the artist could sometimes conceal these defects amongst the strokes of his work; but, when it was to be formed into cups or vases, this could not be done, and for the latter purpose the purest pieces only could be employed.

In the counties of Cornwall and Derby, in the neighbourhood of Bristol, and amongst the mountains of North Wales, small crystals of this kind are frequently found: these are respectively called Cornish, Buxton, Bristol, and Snowdon diamonds. We are informed that the crevices of some parts of Mont Blanc and the Alps contain rock crystal in such abundance as to be perfectly bristled with it.

Some crystals contain in their substance drops of water, or other kind of fluid; and these, as curiosities, are usually sold at a rate considerably higher than others. There are in the British Museum specimens of crystal which enclose many kinds of foreign substances, such as ironstone, needle antimony, and asbestos ([136]).

Various means have been devised for communicating colours to rock crystal. If it be heated and plunged into a solution of indigo, or copper, it acquires a blue colour; or if into a decoction of cochineal, a red colour. A clove-brown colour may be given by exposing it to the vapour of burning wood. Artists sometimes communicate beautiful colours to rock crystals, by forming them into what are called doublets. Two modes of doing this are adopted. In one, a stone that is brilliant-cut at the top is hollowed underneath, filled with the colour that the stone is intended to exhibit, and then closed at the bottom by a plate of glass. If this kind of doublet be dexterously executed, the deception is not easily discovered; for the whole mass will appear of an uniform tint. The second kind of doublet is formed by cementing a coloured plate of glass on the base of a rose or brilliant-cut crystal: by this the whole stone acquires the colour of the plate.