Rhombic pyroxene

Rhombic pyroxene - Mineral, composition (Mg, Fe) SiO3, rhombohedral. FeSiO3: up to 15% - enstatitis, 15 - 50% - hypersten, 50 - 80% - glandular hypersten. In addition to pyroxene cleavage along (110) with an angle of about 90 °, often separate from (010) and (100). The appearance is prismatic. Hardness 5 - 6; specific gravity 3.2 - 3.6. Color from grayish greenish to tombaco-brown and gray-black. Gloss is glass, on the cleavage plane, pearlescent to metallic (bronzite). Nm = 1.65 - 1.75; Ng - Np = 0.009 - 0.017; 2V = + 70 to - 50 ° with a minimum prn 50% FeSiO3. In thin sections, colorless or pleochroic from brownish pink to greenish. Ng [001]. It is common in igneous rocks, most often basic, less often acidic (hypersthene). Impossible in the bulk of effusives and in alkaline rocks. Common in metamorphic high temperature rocks. Impossible with minerals supersaturated with CaO (wollastonite, grossular and others), and alumina silicates (andalusite and others). Glandular hypersthene is very rare.