Diagnostic Features
Hardness: 3
Streak: White
Luster: Nonmetallic pearly
Specific Gravity: 2.6
Cleavage: 3 perfect (rhombohedral) directions at 60 and 120 degrees
Fracture: None
Other: Effervesces vigorously in dilute hydrochloric acid
Identification Tips
1. Calcite resembles dolomite (to which it is chemically related) but is softer and effervesces in hydrochloric acid while dolomite does not.
2. Calcite possesses perfect rhombohedral cleavage. Clear cleaved rhombohedra are referred to as "Iceland Spar" (see picture).
3. Calcite can be translucent to transparent whereas dolomite is only translucent to opaque.
4. Clear cleavage fragments produce doubly refracted images when viewed through the crystal.
5. Calcite is a common sedimentary rock forming mineral, and is the principal constituent of limestone. Calcite is also the principal constituent of marble, the metamorphosed equivalent of limestone.
6. Calcite is only slightly harder then your fingernail but will not scratch glass.
Photographed by Michael P. Klimetz
[Intergrown Cleaved Crystals with Chondrodite (Red) and Graphite (Grey)]
Prices Switch Road
Amity
Orange County
NEW YORK
