orthorhombic Oxides
Chrysoberyl (Cat's Eye)
Formula BeAl2O4
Crystal Structure
orthorhombic[mmm]:{110}@1.0[silk:dense] + {010}@0.8 + {111}@0.5 | phenomenon[chatoyancy] orthorhombic
mmm
{110} {010} {111}
Quick Facts
Hardness
8.5
Specific Gravity
3.7
Refractive Index
1.746
Optical Character
Biaxial +
Physical Properties
- Crystal System
- orthorhombic
- Hardness (Mohs)
- 8.5
- Specific Gravity
- 3.7
- Cleavage
- Good {110}, poor {010}
- Fracture
- Conchoidal to uneven
- Lustre
- Vitreous to subadamantine
Optical Properties
- Refractive Index
- 1.746
- Birefringence
- 0.008-0.010
- Optical Character
- Biaxial +
- Dispersion
- 0.015
- Pleochroism
- moderate: Yellow / Yellow-green / Green (Trichroic (biaxial); more visible in strongly colored stones)
Characteristics
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
When the term "cat's eye" is used alone in gemmology, it refers exclusively to chrysoberyl cat's eye; all other chatoyant gems must be qualified (e.g., "quartz cat's eye")
Related Minerals
Other minerals in the orthorhombic system
