Volltext Seite (XML)
32 HORNBLENDE FAMILY. 3. Preceding figure, in which all the lateral edges are' truncated. 4. Twin-crystal: it may be considered as two flat four-sided prisms joined together by their broad er lateral planes The narrow lateral planes are longitudinally streaked, and glistening : the broad are smooth and splendent. The crystals are middle-sized, small, and very small; are singly imbedded, or intersect one another. The lustre is splendent and pearly. The fracture is broad and slightly curved radiated, sometimes inclining to foliated, and is scopiformly or pro miscuously radiated. The fracture of the crystals is fo liated, with a threefold cleavage: of these cleavages, that parallel with the broad lateral planes is the most distinct; the others are much less so. The cross fracture is un even. The fragments are splintery, or imperfectly rhomboi- dal. It occurs in distinct concretions : the massive varieties in long granular, the radiated in wedge-shaped prismatic concretions. The massive varieties are translucent; the crystals in general transparent. It scratches glass: the broad planes can be scratched with steel; the narrow planes do not yield to it. It is rather brittle. It is easily frangible. Specific gravity, 3.470, Karstcn. 3.517, Saussure. 3.680, Klaproth Physical i . * Disthene double, Hauy.
