HOLOSYMMETRIC CLASS (Holohedral; Pinacoidal.) Here there is only a centre of symmetry. All the forms are pinacoids, each consisting of only two parallel faces. The indices of the three pinacoids parallel to the axial planes are { ioo} , and { o01 } ; those of pinacoids parallel to only one axis are { hko } , { ho/1 and { okl } ; and the general form is { hkl I.
Several minerals crystallize in this class; for example, the plagioclastic felspars, mic rocline, axinite (fig. 65), kyanite, ambly gonite, chalcanthite sasso lite ; among artificial substances are potassium dichromate, racemic acid dibrom-para-nitrophenol, etc.