Calcite

Description:

Calcite (KAL-site) is a mineral species; hexagonal (trigonal) crystal system.

Appearance:

• transparent to opaque
• almost all colors
• phenomena: chatoyancy (in satinspar variety)

Variety and Trade Names:

• marble – granular aggregate occurring in many colors
• onyx marble – banded marble

Identification:

Optic Character: DR, uniaxial negative; AGG 
Refractive Index: 1.486-1.658 
Specific Gravity: 2.70 (+-.05)
Hardness: 3 ; Toughness: poor in single crystals, fair to good in aggregates 

Stone Information from:

Gem Reference Guide, by GIA, ISBN 0-87311-019-6
Gemstones of the world, Third Edition, by Walter Schumann, ISBN 1-4027-4016-6
https://www.gemdat.org/gem-960.html
https://www.mindat.org/min-960.html