Elements of mineralogy, crystallography and blowpipe analysis from a practical standpoint .. . TRAPEZOHEDRAL CLASS. 18. No. 15. Trapezohedral Tetartohedry, Liebisch. No. 22. Trapezohedral Group,ZJowa. Crystals of the common mineral quarj:z are without planes ofsymmetry but are symmetrical to the four axes shown in Fig. 168. The General Form or Trigonal Trapezohedron. nWeiss, na : ——- a?mc; Dana, m-n; Miller, \ hkli\ . Composed of six faces. Fig. 168, each cutting all the axes. Inideal forms these are trapeziums. Fig. 168. Fig. 169.

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