trigonal Oxides
Corundum (Hexagonal Bipyramid)
Al2O3
Quick Facts
Hardness
9.0
Specific Gravity
3.99
Refractive Index
1.762
Optical Character
Uniaxial -
Crystal Structure
#! Species: Corundum
#! System: Trigonal (-3m)
#! Habit: Hexagonal bipyramid with colour zoning
trigonal[-3m]:{10-10}@1.0[colour_zone:hex] + {10-11}@0.8 + {0001}@0.6
trigonal
-3m
{10-10} {10-11} {0001}
Physical Properties
Crystal Systemtrigonal
Hardness (Mohs)9.0
Specific Gravity3.99
CleavageNone (parting on twin planes)
FractureConchoidal to uneven
LustreVitreous to adamantine
Optical Properties
Refractive Index1.762
Birefringence0.008
Optical CharacterUniaxial -
Dispersion0.018
Pleochroismstrong: Body color (darker) / Lighter shade (Blue sapphire shows violet-blue/greenish-blue; ruby shows purplish-red/orange-red)
FluorescenceVariable depending on colour variety
Colours
All colours except red (sapphire)Red (ruby)Colourless (white sapphire)
Localities
MyanmarSri LankaKashmirMadagascarThailandTanzania
Common Inclusions
Rutile silk (three-direction needles)Fingerprints (healed fractures)Hexagonal colour zoningCrystal inclusions (calcite, apatite, zircon)Negative crystals
Known Treatments
Heat treatmentBeryllium diffusionLead glass fillingLattice diffusion
Crystal Forms
prismdipyramidpinacoid
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in Playground #! Species: Corundum
#! System: Trigonal (-3m)
#! Habit: Hexagonal bipyramid with colour zoning
trigonal[-3m]:{10-10}@1.0[colour_zone:hex] + {10-11}@0.8 + {0001}@0.6
Related Minerals
Other minerals in the trigonal system
