Online Encyclopedia

DIHEXAGONAL PYRAMIDAL

Online Encyclopedia
Originally appearing in Volume V07, Page 582 of the 1911 Encyclopedia Britannica.
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DIHEXAGONAL PYRAMIDAL CLASS (Hemimorphic-hemihedral). Six planes of symmetry of two kinds intersect in the hexad axis. The hexad axis is uniterminal and all the forms are open forms. The general form (hikl} consists of twelve faces at oneend of the crystal, and is a dihexagonal pyramid. The hexagonal pyramids {hoTtl} and (h.h.2L.l) each consist of six faces at one end of the crystal. The prisms are geometrically the same as in the holosymmetric class. Perpendicular to the hexad axis are the pedions (000i) and (000I). Iodyrite (Agl), greenockite (CdS), wurtzite (ZnS) and zincite (ZnO) are often placed in this class, but they more probably belong to the hemimorphic-hemihedral class of the rhombohedral division of this system.
End of Article: DIHEXAGONAL PYRAMIDAL
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