ios DOLOMITE FAMILY. 1. Rhomb, in which the faces are sometimes cylin drical^ convex, sometimes cylindrically concave. 2. Lens, both common and saddle-shaped. 3» Flat double three-sided pyramid; is sometimes hollow. 4. Very acute single and double six-sided pyramid. It also occurs in the following supposititious crystals : 1. Rhomb. 2. Double six-sided pyramid. The true crystals are generally small and very small; the supposititious crystals large and middle-sized, and are either hollow, or lined with calcareous-spar. The surface of the crystals is usually drusy, and is sel dom shining, generally glistening or glimmering, and sometimes even dull. Internally it alternates from shining to glistening, and the lustre is pearly. The fracture is generally curved, seldom straight fo liated, with a threefold oblique angular cleavage. The fragments are rhomboidal. The massive varieties occur in granular distinct con cretions, of all the degrees of magnitude, but seldom fine granular: also in straight lamellar concretions, which are very much grown together. It is more or less translucent, passing into translucent on the edges; and the crystals are sometimes perfectly translucent. It is semi-hard ; scratches calcareous-spnr, but neither dolomite nor miemite. It becomes greyish-white in the streak. It is brittle. It is easily frangible. Specific gravity, 2.887, Ilmnj. 2.8S0, Lichlcnberg. Chemical
