HEMIMORPHIC CLASS (Sphenoidal.) In this class the only element of symme try is a single dyad axis, which is polar in character, being dissimilar at the two ends.
The form { 01o} 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 {oio} . The pinacoids {ioo}, {ooi thou} and thou} parallel to the axis of symmetry are geometrically the 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 XYZ and X YZ) ; such a wedge-shaped form is sometimes 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 laevo tartaric 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 ) ; amongst minerals the only example is the hydrocarbon fichtelite (C18H32)•