Analyzer: That part of a polariscope that receives the light after polarization and exhibits its properties. In a petrographic microscope, it is the polarizing mechanism (Nicol prism, Polaroid, etc.) that intersects the light after it has passed through the object under study.
Birefringence: The ability of crystals other than those of the isometric system to split a beam of ordinary light into two beams of unequal velocities; the difference between the greatest and the least indices of refraction of a crystal.
Cross-polarized:
Crystal lattice: The three-dimensional regularly repeating set of points that represent the translational periodicity of a crystal structure. Each lattice point has identical surroundings. There are fourteen possible lattice patterns.
Crystallographic orientation: The relation of the axes or planes of a given crystal to some other established directions in space, e.g., geographic or geologic lines or planes.
Indicatrix: In optics, a geometric figure that represents the refractive indices of a crystal: it is formed by drawing, from a central point representing the centre of a crystal, lines in all directions, whose lengths represent the refractive indices for those vibration directions. The figure for an isotropic crystal is a sphere; for a uniaxial crystal, an ellipsoid of revolution; and for a biaxial crystal, a triaxial ellipsoid (Berry and Mason, 1959, p. 192).
Interference colour: In crystal optics, the colours displayed by a birefringent crystal in crossed-polarized light. Thickness and orientation of the sample and the nature of the light are factors that affect the colours and their intensity.
Plane-polarized: Said of a moving wave, e.g. of light, that has been polarized so that it vibrates in a single plane.
Pleochroism: The ability of an anisotropic crystal to differentially absorb various wavelengths of transmitted light in various crystallographic directions, and thus to show different colours in different directions. This property is more easily seen under polarized light than by the unaided eye. A mineral showing pleochroism is said to be pleochroic.
Polarizer: An apparatus for polarizing light; in a polarizing microscope, it may be the lower Nicol prism or the Polaroid.
Thin section:
A fragment of rock or mineral mechanically
ground to a thickness of approximately 0.03 mm, and mounted between
glasses as a microscope slide. This reduction renders most rocks
and minerals transparent or translucent, thus making it possible
to study their optical properties.