Mineral Information and Data:

Augite
(Ca,Mg,Fe)2(Si,Al)2O6 [CNMNC approved formula]

Named in 1792 from the Greek auge = bright or luster, apparently based on the appearance of its cleavage surface. Strictly speaking, augite is an intermediate member of the Diopside - Hedenbergite solid solution series which the IMA has approved (previously grandfathered) as a mineral species in 2003.

IMA status : Approved Species 2003 ()
CLASSIFICATION 
Dana
(8th edition) :
65.01.03a.03  
  (65) Inosilicate Single-Width Unbranched Chains, W=1
  (65.01) with chains P=2
  (65.01.03a) C2/c clinopyroxenes (Ca clinopyroxenes)
  
Nickel-Strunz
(10th edition) :
09.DA.15
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DA) with 2-periodic single chains, Si2O6; pyroxene family
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 9.70 Å, b = 8.84 Å, c = 5.27 Å, b = 106.97°
Crystal Habit: Crystals short prismatic; massive, granular ,rarely fibrous
Twinning: Common on {100}, contact, simple, repeated; on {001}, lamellar
  
Color: Pale brown to dark brown or purplish brown, greenish, black
Diaphaneity: Transparent to opaque
Luster: Vitreous, resinous to dull
Hardness (Mohs): 5.5 to 6
Measured Density: 3.23 to 3.52 g/cm3
Cleavage: 3; {110} good; {100} and {010} parting
Tenacity: Brittle
Fracture: Uneven to conchoidal
Streak: Grayish green
  
Polymorphism and Series: Isomorphous with Diopside and Hedenbergite
Geologic Setting: Essential in mafic igneous rocks, basalt, gabbro; common in ultramafic rocks; in
some high-grade metamorphic rocks and metamorphosed iron formations.
Mineral Association: Orthoclase, sanidine, labradorite, olivine, leucite, amphiboles, pyroxenes
  
Synonyms/varieties: Fassite (Fe+++, Al-rich var.), ferrohedenbergite, jeffersonite (Mn, Zn-rich var.), violan (Fe=Mg var.), asteroite (Fe-rich var.)
Other Properties: Gemstone Unlikely Available.
Comments: An intermediary member between the solid solution of Diopside and Hedenbergite (which form a series), but contains additional sodium and aluminum impurities. Strictly speaking, Augite is not a single mineral, but a group of closely related minerals identical in structure but containing different percentages of certain elements. However, Augite is scientifically recognized as one mineral species.

 

Augite
Origin: Isle of Ischia, near Naples, Compania, Italy
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Augite
Origin: Borslan, Bohemia, Czech Republic
Sample size: 20 x 13 x 8 mm
Photo: Dan Weinrich

 

Augite
Grey lava infested with 2-3 mm-sized green augite crystals
Origin: San Vito Quarry, Vesuvius, Napoli, Italy
Sample size: 3 x 5 cm
Photo: Diederik Visser

 

Augite
Sharp prismatic single augite crystals or aggregates weathered out of the lava
Origin: Daun, Eifel, Germany
Sample size: thumbnail-size
Photo: Diederik Visser

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