orthorhombic Inosilicates

Bronzite (Cat's-Eye Enstatite)

(Mg,Fe)2Si2O6

Crystal Structure

CDL Notation

 #! 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]

Crystal System orthorhombic

Point Group mmm

Crystal Forms (2)

{110} {001}

Quick Facts

Hardness

5.0

Specific Gravity

3.2

Refractive Index

1.653

Optical Character

Biaxial +

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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.