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(Ca,Mg,Fe)(Mg,Fe,Al)(Al,Si)2O6 A general name for the monoclinic pyroxenes; occurs as dark green to black, short, stubby, prismatic crystals, often of octagonal outline.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
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These lines of evidence include: (a) chilled magmatic enclaves which probably represent the material that mingled with felsic magma, causing thermal and compositional disequilibrium; (b) presence of more and less silicic amphiboles in the same sample, some of them showing reaction textures and inverse zoning; (c) bronzite and hypersthene orthopyroxenes displaying augitic reaction rims, and (d) sieved plagioclase crystals and their occurrence together with clear normal plagioclase, as well as oscillatory zoning of sieved plagioclase.