orthorhombic Inosilicates
Bronzite (Cat's-Eye Enstatite)
(Mg,Fe)2Si2O6
Crystal Structure
#! Species: Cat's-Eye Enstatite (orthopyroxene)
#! System: Orthorhombic (mmm)
#! Habit: Fibrous hollow tube inclusions parallel to c-axis; chatoyancy
orthorhombic[mmm]:{110}@1.0 + {001}@0.4[inclusion:fibrous_tubes]
orthorhombic
mmm
{110} {001}
Quick Facts
Hardness
5.0
Specific Gravity
3.2
Refractive Index
1.653
Optical Character
Biaxial +
Physical Properties
Crystal Systemorthorhombic
Hardness (Mohs)5.0
Specific Gravity3.2
CleavageTwo {110} pyroxene cleavages at ~90° (good)
FractureUneven
LustreSub-metallic (bronzite schiller); vitreous to sub-vitreous (enstatite)
Optical Properties
Refractive Index1.653
Birefringence0.008-0.011
Optical CharacterBiaxial +
Pleochroismweak: Brownish-yellow / Pale brown (Weak trichroism in Fe-bearing material)
Colours
Brownish-green to bronze-coloured with metallic schiller (bronzite)Pale grey to pale green, yellowish-brown (enstatite)Grey-green (cat's-eye enstatite)
Localities
Sri Lanka (cat's-eye enstatite; Embilipitiya and alluvial areas)India (Tamil Nadu; associated with corundum)Myanmar (in gem gravels)
Common Inclusions
Exsolution lamellae of iron oxides (produce bronzite schiller)[object Object]Chromite and other ultramafic minerals
Known Treatments
None known
Crystal Forms
prism
Diagnostic Features
Bronze sub-metallic schiller from oriented iron-oxide exsolution lamellae (diagnostic for bronzite variety); cat's-eye variety (fibrous hollow tube inclusions); biaxial positive; SG 3.20-3.50
Notes
Enstatite (Mg2Si2O6) with significant Fe2+ substitution (bronzite ~10-30 mol% Fe as ferrosilite end-member); formula (Mg,Fe)2Si2O6. Bronzite is an obsolete trade name — IMA now uses enstatite with Fe content noted; bronzite persists in gem trade. Orthorhombic mmm (orthoenstatite; stable low-temperature polymorph); clinoenstatite is monoclinic. Cat's-eye enstatite from Sri Lanka (Embilipitiya) confirmed by Zwaan 1996, Gems & Gemology 32(4):262-269 (DOI 10.5741/gems.32.4.262) [VERIFIED]: "Enstatite, Cordierite, Kornerupine, and Scapolite with Unusual Properties from Embilipitiya, Sri Lanka." Sri Lanka gem island overview: Zwaan 1982 (DOI 10.5741/gems.18.2.62) [VERIFIED]. Constants from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. Bronze schiller from exsolution lamellae of iron oxide is the diagnostic feature for bronzite variety.
Related Minerals
Other minerals in the orthorhombic system
