Calcite
Calcite is the most stable polymorph of calcium carbonate and one of the most common minerals on Earth. It forms limestone, marble, chalk, and most cave formations (stalactites, stalagmites). Its most remarkable property is double refraction — Iceland Spar calcite splits a single light ray into two, creating a doubled image.
Physical Properties
Chemical Formula
CaCO₃
Hardness (Mohs)
3
Color
Colorless, white, yellow, orange, pink, blue, green
Luster
Vitreous to pearly
Crystal System
Hexagonal (trigonal)
Streak
White
Cleavage
Perfect rhombohedral (3 directions)
Specific Gravity
2.71
🔍 Field Identification Tips
Hardness 3 (copper coin scratches it). Three perfect cleavage directions producing rhombohedra. Fizzes vigorously in cold dilute HCl acid — this is the definitive test for calcite. Double refraction visible in clear cleavage pieces (place on text to see doubling).
Varieties & Forms
📍 Where to Find Calcite in the US
Uses & Applications
Construction (limestone, marble), cement, lime production, optical instruments, acid neutralization.
💰 Collector Value Guide
Common calcite: $1–$10. Quality dogtooth calcite on matrix: $20–$200. Iceland Spar: $10–$100. Exceptional cave specimens: $100–$1,000+.
Find Calcite With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.