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 . w > H i-i 1—1 /, N hJ ?n o o >> H , ^ o C/3 f^ .- re o O pq 3. o o pq DEFINITION OF TERMS 83 ature in many crystals alters optical habit, as in Analcitc, in whichdry heat develops double refraction, and thus it appears that theoptical anomalies of this mineral are connected with loss of water,which normally in Analcite reaches over 8 per cent. Optical Anomalies are connected with pseudosymmetry, whichis the assumption of a high
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 . w > H i-i 1—1 /, N hJ ?n o o >> H , ^ o C/3 f^ .- re o O pq 3. o o pq DEFINITION OF TERMS 83 ature in many crystals alters optical habit, as in Analcitc, in whichdry heat develops double refraction, and thus it appears that theoptical anomalies of this mineral are connected with loss of water,which normally in Analcite reaches over 8 per cent. Optical Anomalies are connected with pseudosymmetry, whichis the assumption of a higher order of symmetry by crystals reallylower, through their mimetric juxtaposition or twinning by meansof which they preserve a resemblance to a different system. Thusthe union of three crystals of Aragonite (orthorhombic), producesthe effect of an hexagonal prism. (Fig. 287). Similarly, leucitewhich appears isometric (Fig. 288), would be made, by the meas-urements of von Rath, to be tetragonal. Later observations provedLeucite not to be uniaxial but biaxial and orthorhombic, and againit appeared that when heated this extraordinary mineral becametruly isotropic and cubic. Boracite, apparently cubic, and tetra-hedral, is com
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
