Obsidian
Volcanic Glass (Amorphous Silica) · Semi-Precious Gemstone / Igneous Rock
Crystal System
Amorphous (Non-crystalline); habit is typically massive or pebble-like with conchoidal fractures
Mineral Group
Silicates (Mineraloid)
Chemical Formula
SiO2 (70-75%) with MgO, Fe3O4 trace impurities
Formation Process
Igneous; formed by the rapid cooling of felsic lava, preventing crystal growth
About This Crystal
Jet black to deep grey, opaque to translucent at thin edges, with a highly vitreous (glassy) luster and smooth, curved surfaces
Physical Characteristics
Black body color, white streak, no cleavage, conchoidal fracture, 2.4 specific gravity, non-fluorescent
Optical Properties
Isotropic (singly refractive), refractive index 1.45-1.55, typically no pleochroism or birefringence
Hardness & Durability
Origin Region
United States (Oregon, California), Mexico, Iceland, Italy (Lipari), and Japan; found in volcanic fields
Hardness & Durability
Mohs hardness 5.0-6.0; brittle with low toughness, prone to scratching and chipping
Care & Maintenance
Clean with warm soapy water; avoid ultrasonic cleaners, extreme heat, and contact with harder stones like quartz
Rarity & Value
Common; value depends on variety (sheen, rainbow, snowflake), typically $2-$20 per tumbled specimen
Special Characteristics
Characteristic conchoidal (shell-like) fracture patterns and ability to produce extremely sharp edges
Lore & History
Historically used for arrowheads and mirrors; traditionally associated with protection, grounding, and the root chakra