trigonal Carbonates
Calcite (Nailhead)
CaCO3
Quick Facts
Hardness
3.0
Specific Gravity
2.71
Refractive Index
1.486
Optical Character
Uniaxial -
Crystal Structure
#! Species: Calcite
#! System: Trigonal (-3m)
#! Habit: Nailhead spar (tabular with basal pinacoid)
trigonal[-3m]:{0001}@1.0 + {10-11}@0.4
trigonal
-3m
{0001} {10-11}
Physical 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
pinacoidrhombohedron
Diagnostic Features
Extreme birefringence (0.172); perfect rhombohedral cleavage; effervesces in cold HCl
Notes
Flat tabular habit resembles nail head; often found in limestone cavities
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in Playground #! Species: Calcite
#! System: Trigonal (-3m)
#! Habit: Nailhead spar (tabular with basal pinacoid)
trigonal[-3m]:{0001}@1.0 + {10-11}@0.4
Related Minerals
Other minerals in the trigonal system
