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 . Fig. 362 Fig. 363PlyATE 20 Fig. 364. H O < c < s GUIDE TO COLLECTIONS 163 those formed in crevices which have been filled by crystallizationfrom hot solutions or in limestones which have been altered bycontact with ig-neous rocks. The former are without double re-fraction and the latter exhibit it. The garnets are separated into six varieties, each of which aredistinguished by composition and, to some extent, by color. Theyare: Gr
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 . Fig. 362 Fig. 363PlyATE 20 Fig. 364. H O < c < s GUIDE TO COLLECTIONS 163 those formed in crevices which have been filled by crystallizationfrom hot solutions or in limestones which have been altered bycontact with ig-neous rocks. The former are without double re-fraction and the latter exhibit it. The garnets are separated into six varieties, each of which aredistinguished by composition and, to some extent, by color. Theyare: Grossularite, lime alumina , magnesia alumina , iron alumina , manganese alumina , iron lime , chromium lime garnet. Examples of all of these varieties are exhibited in garnet forms in its more beautiful phases a rich and desirablegem, but is most frequently penetrated by flaws and often includesforeign material or even becomes reduced to a thin shell enclosinga different mineral nucleus. Garnet is a capital illustration of thelaw of substitution, where alumina, iron, chromium and man-ganese, lime
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmineral, bookyear1912
