Augite


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augite

[′ȯ‚jīt]
(mineralogy)
(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.

Augite

 

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 ?
The most common phenocryst silicate phases are olivine, plagioclase and augite, typically, although not always, appearing in that order (Fig.
Opaque minerals occur as inclusions within plagioclase and augite, and as discrete tiny grains in the groundmass.
Calculations used the augite and plagioclase analyses portrayed in Fig.
[FIGURE 7 OMITTED] Table 1 Mineral assemblages for Hurricane Mountain samples, and two samples from Boil Mountain Mafic Felsic 114 158 163 116 147 Augite X X X Serpentine Actinolite X X K-feldspar X X Plagioclase X X X Chlorite X X X X X Epidote X X X X X Pyrite Quartz X X Biotite X X X Muscovite X X Titanite Il-Spinel group X Felsic Ultramafic Boil Mtn.
In tephrite and trachybasalt the phenocryst of plagioclase, augite, olivine, pargasite and phlogopite are embedded in the groundmass of plagioclase, Ti-augite, pargasite, phlogopite, apatite, opaque minerals (ilmenite) and devitrified glass (Sawada et al., 1992).
In 1819 MacNeven described "white augite [diopside] in nearly rectangular prisms" from the Kingsbridge quarry and noted that "[this] was, for a long time, the only locality for this mineral in the United States, but Mr.
Apatite Augite Biotite Calcite Chlorite Chromite Fluorite Galena Hematite Ilmenite Leucoxene Limonite Magnetite Muscovite Olivine Orthopyroxene Pervoskite Phlogopite Pyrite Quartz Serpentine Sphalerite Titanite
The rock they found is an ophitic augite diabase with clay-lined fractures containing well-crystallized "dipyramidal" blue quartz.
Other species include dark green prisms of sodic augite to 3 cm, and 3-4 mm sprays of mordenite.
Simple black prismatic crystals of titaniferous diopsidic augite (Joplin, 1964) reaching 5 mm in length are occasionally observed in the miarolitic cavities associated with the pegmatite schlieren.
Augite phenocrysts more strongly Augite phenocrysts generally pleochroic having purplish-brown, pale-brown and zoning is not as Tirich rims.