Online Encyclopedia

DITRIGONAL BIPYRAMIDAL

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Originally appearing in Volume V07, Page 582 of the 1911 Encyclopedia Britannica.
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DITRIGONAL BIPYRAMIDAL CLASS FIG. 76.—Crystal of a m a m 582 Hexagonal bipyramid of the second order, bounded by twelve faces (s in figs. 99 and 8o) ; indices {II2I} {IO2} . . Dihexagonal prism, consisting of twelve faces parallel to the hexad axis and inclined to the vertical planes of symmetry; indices {hiko}. Hexagonal prism of the first order limo), consisting of six faces parallel to the hexad axis and perpendicular to one set of three vertical planes of symmetry (m in figs. 71, 78-8o). Hexagonal prism of the second order {10o}, consisting of six faces also parallel to the hexad axis, but perpendicular to the other set of three vertical planes of symmetry (a in fig. 78). Basal pinacoid {000t}, consisting of a pair of parallel planes perpendicular to the hexad axis (c in figs. 71, 78-8o). Beryl (emerald), connellite, zinc, magnesium and beryllium crystallize in this class.
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