COMMON HORNBLENDE. 3 appear, and thus there is formed an acumination bf three planes; in other instances, two of the planes disappear, when the acumination is con verted into a bevelmeut, which is either set on the lateral planes, or on the acuter or obtuser lateral edges; and sometimes three of the acu- O T minating planes disappear, when the terminal planes of the prism appear set on obliquely *. The preceding figure, with rounded lateral edges, forming a reed-like crystal. The crystals are long and implanted, sometimes super imposed, and intersecting one another. They are deeply longitudinally streaked, and vary from middle sized to very small. Internally the lustre is shining and pearly. The principal fracture is foliated, with a twofold ob lique angular cleavage, in which the surfaces of the folia are longitudinally streaked: it is often also broad or narrow radiated, and either promiscuous or scopiform. The cross fracture is coarse-grained uneven. The fragments are blunt-edged. The foliated varieties occur in concretions which are large, coarse, and fine, and generally long granular; the radiated varieties in wedge-shaped concretions. The black coloured varieties are opaque, but the green generally translucent on the edges It is intermediate between semi-hard and soft, but more inclining to the first. It yields a inountain-green, inclining to greenish-grey coloured streak. A 2 N It * According to Bournon, the primitive ft*rni of Hornblende is a rhom- Itoidal tetrahedral prism, of 121° 30 and 55° 30, in which the terminal planes* are inclined on the lateral edges 124° 30', so as to form with them ■ngles of 105° and 75°.