WebBiaxial Positive. A mineral is biaxial positive if β is closer to α than to γ.; In this case the acute angle, 2V, between the optic axes is bisected by the γ refractive index direction. Thus we say that γ is the acute bisectrix (BX A), because it bisects this angle.; If a table of optical properties of minerals reports the 2V angle, it usually refers to this acute angle. WebMica Birefringence:.018-.070 (Biotite.04-.07, Lepidolite.018-.038, muscovite.036-.049, zinnwaldite.035) Mica Pleochroism: Biotite is strongly pleochroic in shades of brown or green, fuchsite in shades of green, lepidolite pale violet or green, muscoviteis colorless, zinnwaldite in pale yellow and brown to reddish-brown
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WebRefractive Indices alpha = beta = gamma = delta = 1.614-1.675 1.618-1.691 1.633-1.701 0.019-0.026: ... Hornblende is easly confused with biotite. Distiguishing factors are the lack of birds eye extinction and the … WebRefractive index: nα = 1.712 - 1.718 nβ = 1.720 - 1.725 nγ = 1.727 - 1.734: ... Kyanite occurs in biotite gneiss, ... Kyanite is often used as an index mineral to define and trace a metamorphic zone that was subject to a … flying vulture drawing
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WebMinerals with refractive indices close to 1.54 have low relief, those with much higher or lower refractive indexes will have high relief. (vi) Extinction: angles are only given where minerals usually show a linear feature such as a cleavage and/or long crystal faces. For plagioclase feldspars (stippled) the extinction WebThe refractive index n of a medium (e.g., water, olive oil, etc.), also called the index of refraction, is defined as the quotient of the speed of light in vacuum c and the speed of light in the medium v. It is a dimensionless number that depends on the temperature of the medium and the wavelength of the light beam. WebA petrographic microscope, which is an optical microscope fitted with cross- polarizing lenses, a conoscopic lens, and compensators (plates of anisotropic materials; gypsum plates and quartz wedges are common), for crystallographic analysis. Optical mineralogy is the study of minerals and rocks by measuring their optical properties. flying vulcan