Geoscience Reference
In-Depth Information
In addition, various compensator plates may be inserted
into the light path to determine different optical
properties of minerals. The most commonly used
compensator is the gypsum plate (sensitive tint plate)
which is used for determining the directions of fast and
slow rays in crystals, which is particularly useful for
identifying feldspars. Figures
4-6
provide a comparison
showing the same view of a rock sample in plane-
polarized light, cross-polarized light, and cross-polarized
light with the gypsum plate inserted. Fluorescent dyes
may be added to the consolidating resin during sample
preparation to aid the examination of cracks and pore
structures when the specimen is viewed in combination
with a strong light source and an excitation filter.
4
5
6
4-6
Thin section specimen of dolerite viewed in
plane-polarized transmitted light (
4
), cross-polarized
transmitted light (
5
), and in cross-polarized
transmitted light with the gypsum plate inserted into
the light path (
6
); ×35.
