trigonal Carbonates
Calcite (Rhombohedron)
CaCO3
Crystal Structure
#! Species: Calcite
#! System: Trigonal (-3m)
#! Habit: Rhombohedral cleavage form (Iceland spar)
trigonal[-3m]:{10-11}
trigonal
-3m
{10-11}
Quick Facts
Hardness
3.0
Specific Gravity
2.71
Refractive Index
1.486
Optical Character
Uniaxial -
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Open in PlaygroundPhysical Properties
Crystal Systemtrigonal
Hardness (Mohs)3.0
Specific Gravity2.71
CleavagePerfect rhombohedral {10-11}
FractureConchoidal
LustreVitreous
Optical Properties
Refractive Index1.486
Birefringence0.172
Optical CharacterUniaxial -
Dispersion0.017
PleochroismNone
FluorescenceVariable; red, pink, blue, or green depending on activator ions
Colours
ColourlessYellow (golden dogtooth)WhiteHoney
Localities
USA (Missouri, Tennessee)England (Cumberland)GermanyMexicoChina
Common Inclusions
PhantomsIron oxide stainingFluid inclusions
Crystal Forms
rhombohedron
Diagnostic Features
Extreme birefringence (0.172); perfect rhombohedral cleavage; effervesces in cold HCl
Notes
Extreme birefringence (0.172) causes dramatic double refraction — discovered by Bartholin in 1669
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Open in PlaygroundRelated Minerals
Other minerals in the trigonal system
