Obsidian
Obsidian forms when silica-rich lava cools so rapidly that crystals cannot form — producing a natural volcanic glass. Glass Buttes in Oregon is one of the most popular free rockhounding destinations in the country — a BLM site covered in obsidian of every variety. Apache Tears from Arizona are small rounded obsidian nodules found loose in the desert and prized by collectors.
Physical Properties
Chemical Formula
Volcanic glass (amorphous)
Hardness (Mohs)
5–5.5
Color
Black, mahogany, rainbow, snowflake (white inclusions)
Luster
Vitreous
Crystal System
None (amorphous)
Streak
White
Cleavage
None (conchoidal fracture)
Specific Gravity
2.35
🔍 Field Identification Tips
Jet black, glassy luster, extreme sharpness when broken (sharper than any metal blade). No crystals. Lighter than most rocks (SG 2.35). Conchoidal fracture produces curved, shell-like breaks. Distinguished from black tourmaline by lack of crystal structure and much smoother luster.
Varieties & Forms
📍 Where to Find Obsidian in the US
Uses & Applications
Surgical scalpel blades (sharper than steel), arrowheads, jewelry, decorative carvings. Historically used for cutting tools.
💰 Collector Value Guide
Common black: $1–$5/lb. Rainbow obsidian: $5–$50. Mahogany slabs: $10–$100. Apache Tears: $1–$5 each.
Find Obsidian With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.