Also found in: Dictionary, Thesaurus, Wikipedia.


(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.



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.

References in periodicals archive ?
Petrographic thin sections are dominated by anhedral Ca-rich augite and subhedral to euhedral calcic plagioclase laths in a subophitic
Unit G is oniy slightly porphyritic and has analcite and ophitic augite, which A does not).
Mason, Pyrope, augite, and hornblende from Kakanui, New Zealand, New Zealand J.
Although we would not suggest that the diopside (Di) was actively formed by metamorphic processes, the destruction of the Fe-Mg components of augite will make the remaining pyroxene more calcic.
Augite phenocrysts more strongly Augite phenocrysts generally pleochroic having purplish-brown, pale-brown and zoning is not as Tirich rims.
Furthermore, minerals common to both series (chromite, olivine, augite, plagioclase, magnetite and ilmenite) are compositionally distinct reflecting fundamental chemical differences between the two magma series.
Coughlan (1986) recognized five units in the Staples Mountain Gabbro, designated I to V from inferred bottom to top: I--gabbro, anorthositic gabbro, and olivine gabbro; II--subophitic augite gabbro; III--interlayered norite and anortbosite; IV--unlayered augite gabbro and minor olivine gabbro; V --unlayered gabbronorite, with increased orthopyroxene and no olivine, in contrast to unit IV.
The samples, which ate all very similar, contain augite ([less than or equal to] 5mm, ~[Wo.
Relict igneous pyroxene of hypersthene composition was observed in rare gabbroic samples, whereas the later diabase dykes contain augite.
A typical mineral assemblage for mafic samples includes augite, albite, chlorite, epidote, biotite, and ilmenite-spinel.
Petrographically, the basalts are described as containing calcic plagioclase, augite, and rarer pigeonite and bronzite, and Fe-Ti oxides, and vary from holocrystalline to variably vitrophyric ([less than or equal to]30%).
2006, High-Ca augites do not prove that komatiites were wet: American Geophysical Union, Fall Meeting, 2006, abstract V24B-04.