Abstract

Polarization figures given by opaque minerals in convergent reflected light are described, and an explanation of the figures is offered. Three properties of isotropic opaque minerals determinable from polarization figures are defined: the strength of dispersion of the reflection rotation, the relative dispersion of the reflection rotation, and the dispersion of the ellipticity. These properties are related to the rotation of the vibration planes of incident convergent plane-polarized rays by reflection from polished surfaces or crystal faces of isotropic minerals. Isotropic minerals differ in dispersion properties; hence the properties can be used as an aid in identification.Six properties of anisotropic minerals determinable from their polarization figures are defined: the sense of rotation of incident plane-polarized light with respect to known crystallographic elements, the degree of dispersion of the reflection rotation, the relative dispersion of the reflection rotation, the apparent angle of rotation due to anisotropy of the mineral, the amount of dispersion of the apparent angle of rotation, and the relative dispersion of the apparent angle of rotation. Opaque anisotropic minerals differ in their rotation properties; the properties can therefore be used for distinguishing them.Procedures for analysis of polarization figures are described and the results of observations of polarization figures for a group of about 40 isotropic and anisotropic opaque minerals are given. The technique appears to offer material aid in the identification of ore minerals, the more so because analysis of polarization figures is quickly and readily done.

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