There follows a series of examples of minerals with various refraction indices.
As shown in the INTRODUCTION to this program the microscopic preparations of the rocks and soils are made up of thin slices of the samples, around 30mm thick. On the other hand, the fine sand minerals (200-20 micras) are studied under the petrographic microscope by mounting the grains directly in an inclusion cement.
These two different forms of microscopic preparations (slices for rock minerals and whole grains for fine sand minerals) mean that the degree to which relief appears does not correspond exactly. The sand grains often present spherical or ellipsoidal shapes and great thicknesses. Both characteristics accentuate the relief of the grains. Because of this, for a same degree of relief, the relief is often presents more contrast in the sand grains than in a thin section of rock or soil belonging to the same mineral.
In test type A, 6 grains are shown which must be ordered in a sequence of increasing relief (8 test type A).
Test type B shows an image of a mineral, and the degree of relief which it presents must be evaluated (40 test type B).
In the first examples of test B for each type of microscopic preparation (sand grains or rock minerals) there exists the possibility of using a scale of standard minerals for each degree of relief.
Test type C shows an image of a rock mineral, and the degree of relief which it presents must be evaluated (30 test type B).
Firstly, the tests corresponding to the sand grains will be shown, which are easier to evaluate.
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