Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V07, Page 579 of the 1911 Encyclopedia Britannica.
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HEMIMORPHIC CLASS (Sphenoidal). In this class the only element of symmetry is a single dyad axis, which is polar in character, being dissimilar at the two ends. The form (0101 perpendicular to the axis of symmetry consists of a single plane or pedion; the parallel face is dissimilar in character and belongs to the pedion {oio1. The pinacoids 1100), tool}, {hol} and (hol} parallel to the axis of symmetry are geometrically the From µ6VOt, single, and KXLVSLP, to incline, since one axis is inclined to the plane of the other two axes, which are at right angles.same in this class as in the holosymmetric class. The remaining forms consist each of only two planes on the same side of the axial plane XOZ and equally_ inclined to the dyad axis (e.g. in fig. 62 the two planes X YZ and X YZ) ; such a wedge-shaped form is some-times called a sphenoid. Fig. 64 shows two crystals of tartaric acid, a a right-handed crystal of dextro-tartaric acid, and b a left-handed crystal of laevotartaric acid. The two crystals are enantiomorphous, i.e. although they have the same interfacial angles they are not superposable, one being the mirror image of the other. Other examples are potassium dextro-tartrate, cane-sugar, milk-sugar, quercite, lithium sulphate (Li2SO4•H20); amongst minerals the only example is the hydrocarbon fichtelite (CbH8).
End of Article: HEMIMORPHIC

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