trigonal Oxides
Ruby
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 -
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Open in PlaygroundPhysical Properties
Crystal Systemtrigonal
Hardness (Mohs)9.0
Specific Gravity4.0
CleavageNone (parting on {0001})
FractureConchoidal to uneven
LustreVitreous to adamantine
Optical Properties
Refractive Index1.762
Birefringence0.008
Optical CharacterUniaxial -
Dispersion0.018
Pleochroismstrong: Purplish-red / Orange-red (Best seen in thick stones; dichroism key to separating from red spinel)
FluorescenceModerate to strong red (LWUV); weaker under SWUV
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
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Open in PlaygroundSynthetics & 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
