trigonal Oxides
Sapphire
Al2O3:Fe,Ti
Crystal Structure
#! Species: Sapphire (Corundum)
#! System: Trigonal (-3m)
#! Habit: Barrel-shaped with horizontal striations
trigonal[-3m]:{10-10}@1.0[striation:horizontal] + {10-11}@0.7 | elongate(c:1.8) | [silk:dense]
trigonal
-3m
{10-10} {10-11}
Quick Facts
Hardness
9.0
Specific Gravity
3.99
Refractive Index
1.762
Optical Character
Uniaxial -
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Open in PlaygroundPhysical Properties
Crystal Systemtrigonal
Hardness (Mohs)9.0
Specific Gravity3.99
CleavageNone (parting along twin planes)
FractureConchoidal to uneven
LustreVitreous to adamantine
Optical Properties
Refractive Index1.762
Birefringence0.008
Optical CharacterUniaxial -
Dispersion0.018
Pleochroismstrong: Violetish-blue / Greenish-blue (Stronger in darker stones; best observed through dichroscope)
FluorescenceVariable; blue often inert; chalky blue-green SWUV in some Sri Lankan
Colours
BlueYellowPinkOrangeGreenPurpleColorlessPadparadscha (pink-orange)
Localities
Kashmir, IndiaMyanmar (Mogok)Sri Lanka (Ceylon)MadagascarAustraliaMontana, USA
Common Inclusions
Rutile silkFingerprintsCrystal inclusions (calcite, apatite, zircon)Hexagonal zoningNegative crystals
Known Treatments
Heat treatmentBeryllium diffusionLead glass fillingFlux healing
Crystal Forms
prismdipyramid
Diagnostic Features
Hexagonal growth zoning; colour banding; silk (rutile needles at 60°); iron absorption bands
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Open in PlaygroundSynthetics & Simulants
Known synthetic and simulant versions of Sapphire
Related Minerals
Other minerals in the trigonal system
