trigonal Carbonates
Calcite (Nailhead)
CaCO3
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}
Quick Facts
Hardness
3.0
Specific Gravity
2.71
Refractive Index
1.486
Optical Character
Uniaxial -
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
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
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 PlaygroundRelated Minerals
Other minerals in the trigonal system
