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 . ection parallelto the plane of the optic axes neither optical axis nor the ring sys-tem will be seen, but only curved black bands. A section oblique toeither the acute bisectrix or the obtuse bisectrix, will produce partialring systems as in Fig. 278 (Miers). Further it is to be expected that the optical axes, and hencethe axial angle, in the biaxial crystals will be different for differ-ent colored light; and they are. This is technica
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 . ection parallelto the plane of the optic axes neither optical axis nor the ring sys-tem will be seen, but only curved black bands. A section oblique toeither the acute bisectrix or the obtuse bisectrix, will produce partialring systems as in Fig. 278 (Miers). Further it is to be expected that the optical axes, and hencethe axial angle, in the biaxial crystals will be different for differ-ent colored light; and they are. This is technically called dis-persion of the axes, and in the orthorhombic system the opticalaxes, and the curved bands for blue and red light, appear betweencrossed nicols, separated from each other along the same line(Fig. 279) in which R. stands for red light, and B. for blue light;while in white light this dispersion effect produces a superimposi-tion of the figures of the single colors, and the brush will lie betweenB. and R. in Fig. 279 (after Miers). The optical axes are, of course,in one plane, and in the orthorhombic minerals that plane is a planeof Fig. 279 In monoclinic crystals the dispersion effects are more compli-cated, and there has been noted crossed dispersions, (Fig. 280,after Miers), horizontal dispersion, (Fig. 281, after Miers) andinclined dispersion, (Fig. 282, after Miers). In the monoclinic
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
