augite

Augite is a single chain inosilicate mineral described chemically as (Ca,Mg,Fe)SiO3 or calcium magnesium iron silicate. The crystals are monoclinic and prismatic. Augite has two prominent prismatic cleavages, meeting at angles near 90°. Augite is a solid solution in the pyroxene group. Diopside and hedenbergite are important endmembers in augite, but augite can also contain significant aluminium, titanium, and sodium and other elements. The calcium content of augite is limited by a miscibility gap between it and pigeonite and orthopyroxene: when occurring with either of these other pyroxenes, the calcium content of augite is a function of temperature and pressure, but mostly of temperature, and so can be useful in reconstructing temperature histories of rocks. With declining temperature, augite may exsolve lamellae of pigeonite and/or orthopyroxene. There is also a miscibility gap between augite and omphacite, but this gap occurs at lower temperature and is not well understood.
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Noun
1. dark-green to black glassy mineral of the pyroxene group containing large amounts of aluminum and iron and magnesium
(hypernym) mineral

(n.)
A variety of pyroxene, usually of a black or dark green color, occurring in igneous rocks, such as basalt; -- also used instead of the general term pyroxene.
  

General Information:
 Chemical Formula:
(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
 Environment:
Basic igneous and metamorphic rocks.
 IMA Status:
Approved IMA 1980
 Locality:
Common world wide.
 Name Origin:
From the Greek auge - "luster."
Physical Properties:
 Cleavage:
[110] Perfect, [010] Indistinct
 Color:
brown green, green, light brown, dark brown, or black.
 Density:
3.2 - 3.6, Average = 3.4
 Diaphaniety:
Translucent to opaque
 Habits:
Massive - Fibrous - Distinctly fibrous fine-grained forms., Columnar - Forms columns, Granular - Generally occurs as anhedral to subhedral crystals in matrix.
 Hardness:
5-6.5
 Luminescence:
Non-fluorescent.
 Luster:
Vitreous - Resinous
 Streak:
greenish gray
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augite
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