Описание
2 1 Background
appropriate choice for microscopic investigation, in view of its very fine grainsize. He described and suggested a mechanical origin for slaty cleavage (Sorby,
1853, 1856), noticed many of the basic features of igneous and metamorphic
rocks, made many important observations on sedimentary rocks, including
carbonate rocks (Sorby, 1851, 1879), investigated pressure-solution (using fossil
crinoids), described meteorites, and published the first papers on the examination
of polished sections of metals with the microscope (Sorby, 1864, 1887). So not
only is he the founder of petrography (the description of rocks), but the founder
of metallography as well (Smith, 1960). He also investigated fluid inclusions in
minerals, heating crystals to watch the gas bubbles disappear, in order to get an
estimate of the temperature of crystallization of the mineral (Sorby, 1858; Folk,
1965).
Sorby was followed soon after by many others, as discussed by Johannsen
(1939) and Loewinson-Lessing (1954). Among them were Dawson (1859), Zirkel
(1863, 1866, 1876), Vogelsang (1867), Fouqué& Michel-Lévy (1879), Allport
(1874), Rosenbusch (1873, 1877) and Teall (1885, 1886). Since those days, the
light microscope has become the main tool for identifying minerals and examining their microstructures, although it has been augmented by many modern
techniques (Section 1.6).
1.3 How relevant is the microscope today?
Many petrologists concentrate on the mineralogical and chemical aspects of rocks,
without spending much time looking at rocks with the microscope. In fact, in
these days of marvellous techniques for the chemical and isotopic analysis of
minerals, some people may feel that simply looking at and measuring the shapes
and arrangements of crystals in rocks with the microscope is a little out of date.
However, carrying out detailed chemical and isotopic analyses of minerals when
you don’t understand the relationships of these minerals to other minerals in the
rock makes little sense. It’s a waste of expensive resources, at very least.
On the other hand, many structural geologists look at the physical or structural
aspects of minerals and rocks, especially from the viewpoint of deformation
processes and preferred orientations of grains, without being concerned about
the chemical aspects of these processes. Both approaches are valuable, of course,
but their interrelationships can be particularly illuminating. Fortunately, many
researchers are attempting to integrate the chemical and physical approaches,
and the study of rocks with the microscope provides a link between them. In
fact, the detailed study of processes in rocks at the microscopic scale is now a
major area of research, especially among younger people, in many universities
and other research institutions. Moreover, new observational techniques are being
developed and used, as discussed in Section 1.6.
Research microscopes commonly have both transmitted and reflected light
facilities. An excellent example of the simultaneous use of transmitted and
Детали
- Год издания
- 2004
- Format