trigonal Oxides
Ruby
Formula Al2O3:Cr
Crystal Structure
#! Species: Ruby (Corundum)
#! System: Trigonal (-3m)
#! Habit: Tabular with dipyramid and oriented silk
trigonal[-3m]:{10-11}@1.0[silk:oriented] + {0001}@0.4
trigonal
-3m
{10-11} {0001}
Quick Facts
Hardness
9.0
Specific Gravity
4.0
Refractive Index
1.762
Optical Character
Uniaxial -
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 9.0
- Specific Gravity
- 4.0
- Cleavage
- None (parting on {0001})
- Fracture
- Conchoidal to uneven
- Lustre
- Vitreous to adamantine
Optical Properties
- Refractive Index
- 1.762
- Birefringence
- 0.008
- Optical Character
- Uniaxial -
- Dispersion
- 0.018
- Pleochroism
- strong: Purplish-red / Orange-red (Best seen in thick stones; dichroism key to separating from red spinel)
- Fluorescence
- Moderate to strong red (LWUV); weaker under SWUV
Characteristics
Colours
RedPinkish-redPurplish-red
Localities
MyanmarMozambiqueThailandMadagascar
Common Inclusions
SilkCrystalsFingerprintsColor zoning
Known Treatments
Heat treatmentGlass fillingFlux healing
Crystal Forms
dipyramidpinacoid
Diagnostic Features
Strong red fluorescence (LWUV); silk (rutile needles at 60°); absorption at 694nm doublet
Synthetics & Simulants
Known synthetic and simulant versions of Ruby
Flux-Grown Ruby (Crystal) synthetic
Flux
Hydrothermal Ruby (Crystal) synthetic
Hydrothermal (autoclave; Aqueous HF/chloride Mineraliser; Cr Dopant; Seed Plate Of Natural Or Synthetic Corundum; 400-500 Degrees C / >1 Kbar)
Kashan Flux Ruby (Crystal) synthetic
Flux (molybdate-based Flux In Platinum Crucible; Slow-cooling Crystallisation; Independently Developed From Chatham Process)
Synthetic Ruby (Verneuil) (Boule) synthetic
Flame Fusion
Related Minerals
Other minerals in the trigonal system
