Augite

Augite
Augite – Muhavura volcano
General
Category	Inosilicates
Formula (repeating unit)	(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6
IMA symbol	Aug[1]
Strunz classification	9.DA.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 9.699, b = 8.844 c = 5.272 [Å] β = 106.97°; Z = 4
Identification
Color	Black, brown, greenish, violet-brown; in thin section, colorless to gray with zoning common
Crystal habit	Commonly as stubby prismatic crystals, also acicular, skeletal, dendritic
Twinning	Simple or multiple on {100} and {001}
Cleavage	{110} good with 87° between {110} and {110}; parting on {100} and {010}
Fracture	uneven to conchoidal
Tenacity	brittle
Mohs scale hardness	5.5 to 6
Luster	Vitreous, resinous to dull
Streak	Greenish-white
Diaphaneity	Transparent to opaque
Specific gravity	3.19–3.56
Optical properties	Biaxial (+)
Refractive index	nα = 1.680–1.735, nβ = 1.684–1.741, nγ = 1.706–1.774
Birefringence	δ = 0.026–0.039
Pleochroism	X = pale green, pale brown, green, greenish yellow; Y = pale brown, pale yellow-green, violet; Z = pale green, grayish green, violet
References	[2][3][4]

Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.