Augite(redirected from augitic)
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a mineral of the pyroxene group.
In chemical composition and crystalline structure, augite belongs to the chain silicates. Its approximate chemical formula is (Ca, Na) (Mg, Fe”, Fe”’, Al, TI) [(Si, A1)2O6]. It forms short prismatic or flattened isometric crystals of the monoclinic system with good prismatic cleavage along two surfaces that intersect at an angle of 87–88°. Its density is between 3,200 and 3,600 kg/m3. Its hardness is five or six on the ten-degree scale. Augite is greenish black, with a glassy luster. The mineral develops by crystallization from magmatic melts as a rock-forming mineral in many igneous rocks. It is converted to hornblende (uralite) or chlorite when altered by the action of hydrothermal solutions, and to the free oxide Si02 (opal), iron hydroxide, carbonates, and argillaceous halloysite and nontronitic products by weathering.