Optical Mineralogy Lab 14 Fall 2012 Biaxial Interference Figures Biaxial interference figures in mineralogy this document discusses how to determine the optic sign and estimate the 2v angle of biaxial minerals using optical mineralogy. There are three methods for determining the optic sign of a biaxial mineral using an interference figure: biaxial (bxa) figure, centered optic axis (oa) figure, and off centered bxa or oa figure.
Optical Mineralogy Lab 14 Fall 2012 Biaxial Interference We can get interference figures from all grains, but interpreting them can be difficult or impossible. with care, however, we can identify three different kinds of useful figures: optic axis figures (oa), acute bisectrix figures (bxa), and optic normal figures (on). Lab 14 – fall, 2012 biaxial interference figures. optical mineralogy. biaxial sign: b x a figures. to determine the optic sign of a biaxial mineral from a bx a figure, position the isogyres so that the melatopes are in the ne and sw quadrants. For optically negative minerals, bxo is the z axis and nbxo = nγ, and corresponds to the slow ray. must determine whether the ray vibrating parallel to the obtuse bisectrix is the fast or slow ray. obtain an acute bisectrix interference figure. Explore biaxial mineral optics: rvs, indicatrix, orientation, optic figures, and sign determination. college level mineralogy lecture notes.
Optical Mineralogy Lab 14 Fall 2012 Biaxial Interference For optically negative minerals, bxo is the z axis and nbxo = nγ, and corresponds to the slow ray. must determine whether the ray vibrating parallel to the obtuse bisectrix is the fast or slow ray. obtain an acute bisectrix interference figure. Explore biaxial mineral optics: rvs, indicatrix, orientation, optic figures, and sign determination. college level mineralogy lecture notes. ÿÀ ÈÈ " ÿÄ ÿĵ } !1a qa "q 2 ‘¡ #b±Á rÑð$3br‚ %&'()*456789:cdefghijstuvwxyzcdefghijstuvwxyzƒ„…†‡ˆ‰Š’“”•–—˜™š. Both parts of the thinner band narrow at the points of incidence of the optic axes (known as melatopes) and these are represented in the figure 1 by the letters a and b. These videos were made as virtual samples for an undergraduate optical mineralogy related course. each video shows a full 360 degree rotation of the microsco. Interference figures reveal optic axis orientation. you obtain them by inserting the bertrand lens (or removing the ocular) under crossed polars with the condenser fully engaged. a centered uniaxial figure shows a dark cross, while a centered biaxial figure shows curved dark bands (isogyres).
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