Fluorite
Fluorite is one of the most colorful and collectible minerals — a single specimen can display purple, green, yellow, and blue in perfect cubic crystals. Illinois was historically the world's largest fluorite producer and the mineral is the state mineral. Fluorite is the origin of the word "fluorescence" — many specimens glow brilliant blue under UV light.
Physical Properties
Chemical Formula
CaF₂
Hardness (Mohs)
4
Color
Purple, green, yellow, blue, colorless, pink — often multicolored
Luster
Vitreous
Crystal System
Cubic (isometric)
Streak
White
Cleavage
Perfect octahedral (4 directions)
Specific Gravity
3.18
🔍 Field Identification Tips
Hardness 4 (steel knife scratches it easily, copper coin does not). Perfect cubic cleavage — freshly broken pieces show flat triangular cleavage faces. Distinguished from amethyst by cleavage and lower hardness. Check with UV light — most fluorite fluoresces strongly blue.
Varieties & Forms
📍 Where to Find Fluorite in the US
Uses & Applications
Flux in steel making, hydrofluoric acid production, optics (CaF₂ lenses), decorative carvings, collectors.
💰 Collector Value Guide
Illinois pocket fluorite: $20–$500. Mexican green/yellow: $30–$300. Rainbow fluorite: $10–$100. English Blue John: $50–$500+.
Find Fluorite With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.