A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . es ofcolored curves, which in uniaxial crystals, cut atright angles to the optic axis, are seen as con-centric rings, while crossing these rings is a blackcross. This cross results from the absence ofdouble refraction along the optic axis of the crys-tal, and consequently the extinction or absorptionof the light in the analyzer in two directionsat right angles to each other. In all other directions there is interferenceand hence color r
A popular guide to minerals : with chapters on the Bement Collection of minerals in the American Museum of Natural History, and the development of mineralogy . es ofcolored curves, which in uniaxial crystals, cut atright angles to the optic axis, are seen as con-centric rings, while crossing these rings is a blackcross. This cross results from the absence ofdouble refraction along the optic axis of the crys-tal, and consequently the extinction or absorptionof the light in the analyzer in two directionsat right angles to each other. In all other directions there is interferenceand hence color rings. In converging light in asection cut at right angles to an optical axis ofa biaxial crystal, a black bar intersecting oval ringsis seen. In the case of a section inclined to the opticaxes in a biaxial crystal a very different aspect isgiven to the slide. The rings become lemniscate, then perhapsunite in an 8-shaped figure, then separate into long arms. show this in thin and thinner sheets of mica, the figuresomewhat expanding, as the section becomes thinner, as a longerdistance must be traversed by the rays before interference, produc-. Fig. 273
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
