Obsidian
Obsidian (Amorphous Volcanic Glass) · Minor Gemstone / Volcanic Glass
Crystal System
Amorphous (No crystal system); massive, blocky, or nodular habit
Mineral Group
Silicates (Non-crystalline mineraloid)
Chemical Formula
SiO2 (approx. 70–75%) with MgO, Fe3O4, and Al2O3
Formation Process
Extrusive igneous; forms from the rapid cooling of felsic lava, preventing crystal growth
About This Crystal
A dark, glass-like volcanic rock. It exhibits a smooth, uniform texture with a vitreous (glassy) luster and translucent edges when thin.
Physical Characteristics
Color: Typically black or dark grey; Streak: White; Fracture: Conchoidal (shell-like); Specific Gravity: 2.4; Luster: Vitreous
Optical Properties
Isotropic (Singly refractive); Refractive Index: 1.450–1.550; No pleochroism or birefringence
Hardness & Durability
Origin Region
Volcanic regions including USA (Oregon, California), Mexico, Iceland, and Greece (Milos)
Hardness & Durability
Mohs Hardness: 5 to 6; brittle tenacity; low toughness due to glass-like nature and shell-like fracturing
Care & Maintenance
Clean with warm soapy water; avoid ultrasonic cleaners and mechanical impacts; store separately to prevent scratches
Rarity & Value
Common; value is generally low except for specimens with sheen (Gold, Silver) or color-play (Rainbow)
Special Characteristics
Displays conchoidal fracturing creating razor-sharp edges; sometimes shows snowflake inclusions or iridescence
Lore & History
Historically used for arrowheads and ritual blades; traditionally associated with protection, grounding, and revealing truth