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 . >> 2 rt tM o X >, u t> en 3 ffi o S a* I/. ^ J ,- rs ^ - m ri w -> <^ rt , c u .2 DEFINITION OF TERMS. to the assumed axes. Prof.Heddle furnishes a strikingillustration of polar tendencies(Fig 7), in a crystal of pyrite(pentagonal dodacahedron),which has attached to it in reg-ular alternation, at the extrem-ities of the assumed axes, smallcrystals of the same form. Diversity of crystallizedforms is one of the most ob-
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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 . >> 2 rt tM o X >, u t> en 3 ffi o S a* I/. ^ J _, - rs ^ - m ri w -> <^ rt , c u .2 DEFINITION OF TERMS. to the assumed axes. Prof.Heddle furnishes a strikingillustration of polar tendencies(Fig 7), in a crystal of pyrite(pentagonal dodacahedron), which has attached to it in reg-ular alternation, at the extrem-ities of the assumed axes, smallcrystals of the same form. Diversity of crystallizedforms is one of the most ob-vious features of mineralogicaloccurrences, but examples arefound in nature where differ-ently formed crystals are en-cased within each other, point-ing to a crystallographic identity. In Fig. 8 such an instance isshown, a scalenohcdron of calcite, supporting at its apex arhombohedron of the same mineral, the two enclosed in a largercrystal of calcite made up of a hexagonal prism and a rhombo-hedron; and geometrical analysis shows that the scalenohcdron, therhombohedron and the prism are referable toone crystal system. In Crystals an intensityof cohesion, of hardness, etc., is discoveredin certain directions; the action of light, the electric reactions, the rate of decay, is