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Augite (Photo) [abbr. Aug ]

Year of discovery: 1792 (World), 1895 (Japan)

Locality list: 1,095 localities of augite

• (Ca,Mg,Fe)₂Si₂O₆
• (Ca,Na)(Mg,Fe²⁺,Al,Fe³⁺,Ti)(Si,Al)₂O₆
• [(Ca,Mg,Fe)²⁺₂][(SiO₃)₂]^4-
• Ca/(Mg+Fe+Ca)=0.2-0.45

• Class: Ca-Mg-Fe pyroxene group < Pyroxene supergroup
• Class: Inosilicate (Single chain)
• Variety: Titanaugite (+Ti)
• Variety: Asteroite (+Fe)
• Variety: Fassaite (-Fe)
• Variety: Calc-pigeonite (+Ca)
• Variety: Pigeonite-augite (+Ca)
• Variety: Enstatite-diopside (+Mg)
• Variety: Endiopside (+Mg)
• Insoluble in: HCl
• Substitution pseudomorph: Replaced by amphiboles such as Actinolite. (Uralite)

• Ca/(Mg+Fe+Ca) < 0.2: Pigeonite
• Ca/(Mg+Fe+Ca) > 0.45, Mg > Fe: Diopside
• Ca/(Mg+Fe+Ca) > 0.45, Fe > Mg: Hedenbergite

• Color: Dark green
• Streak: Greenish gray
• Luster: Vitreous
• Diaphaneity: Translucent-Opaque

• Habit: Short prismatic
• Twin: Contact twin, Intrusive twin

• Cleavage: Perfect on {110} (2 planes, 90 degree), Parting on {100} and {010} (2 planes)
• Hardness: 5.5-6
• Density: 3.5

• System: Monoclinic
• Group: 2/m, C2/c
• Lattice: a=9.7, b=8.8, c=5.3, a^c=107.0

Etymology: Auge (luster) in Greek

Synonym: Aegirine-hedenbergite, Anthochroite, Ferroaugite, Ferrohedenbergite, Korea-augite