trigonal Carbonates
Calcite (Rhombohedron)
Formula 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 -
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 3.0
- Specific Gravity
- 2.71
- Cleavage
- Perfect rhombohedral {10-11}
- Fracture
- Conchoidal
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.486
- Birefringence
- 0.172
- Optical Character
- Uniaxial -
- Dispersion
- 0.017
- Pleochroism
- None
- Fluorescence
- Variable; red, pink, blue, or green depending on activator ions
Characteristics
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
Related Minerals
Other minerals in the trigonal system
