orthorhombic Oxides
Chrysoberyl (Tabular Twin)
BeAl2O4
Quick Facts
Hardness
8.5
Specific Gravity
3.7
Refractive Index
1.746
Optical Character
Biaxial +
Crystal Structure
orthorhombic[mmm]:{110}@1.0 + {010}@0.8 + {111}@0.5 orthorhombic
mmm
{110} {010} {111}
Physical Properties
Crystal Systemorthorhombic
Hardness (Mohs)8.5
Specific Gravity3.7
CleavageGood {110}, poor {010}
FractureConchoidal to uneven
LustreVitreous to subadamantine
Optical Properties
Refractive Index1.746
Birefringence0.008-0.010
Optical CharacterBiaxial +
Dispersion0.015
Pleochroismmoderate: Yellow / Yellow-green / Green (Trichroic (biaxial); more visible in strongly colored stones)
Colours
Yellow-green (chrysoberyl)Golden yellowBrownGreen
Localities
Brazil (Minas Gerais)Sri LankaMadagascarTanzaniaRussia (Ural - historic alexandrite)Zimbabwe
Common Inclusions
Silk (needle-like, for cats-eye)Stepped twin planesCrystal inclusionsFingerprints
Known Treatments
Generally untreated
Crystal Forms
prismpinacoiddipyramid
Notes
Pseudohexagonal trillings common due to cyclic twinning; cats-eye chrysoberyl is the finest chatoyant gem
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