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 ?
Petrographic examination with crossed-polarized light clearly shows that augite grains of the Titanic headstones and Hanson quarry are optically, and therefore chemically, strongly zoned.
They are high iron tholeiitic dolerites with strongly zoned pyroxenes (pigeonite, augite, ferroaugite).
As an example, our rule for augite (AGT) has requirements on the ions of iron (Fe), titanium (Ti) and Ca.
Mineral augite augite biotite ilmenite ilmenite Analysis 637/15 637/16 637/13 637/1 637/2 Si[O.
is a dense porphyritic basalt with about twenty percent of tabular plagioclase and minor augite and olivine phenocrysts.
At the same time a large crystal of Cr-bearing augite became available with approximately 0.
5 mm) vessel fragment exposes plagioclase (the white, long and narrow mineral grains at the edge), and augite and olivine (in the centre of the photograph, you can see the olivine is largest).
The combined optical and SEM/EDX work shows that the heavy minerals in the MPH sandstone consist of (by weight) diopside (59%), calcic amphibole (25%), ahnandine-rich garnet (5%), and a few less abundant phases including augite, talcminnesotaite, grossular-rich garnet, and Fe-Ti oxide.
These holes are in the same geological location as the Malachite Zone along the contact of the augite syenite and the Two Duck Lake gabbro but are one kilometer to the south of the Malachite Zone.
The dyke rock has a distinctive cross-columnar field appearance, and a subophitic to micro-porphyritic texture with abundant Ti-bearing augite, calcic plagioclase, scattered euhedral orthopyroxene phenocrysts, and coarse-grained glomerophyric clumps of augite with plagioclase.
The result reveals that Quarts, Calcite and Feldspar are major minerals while Hematite and Augite are secondary ones (Table 2).