Obsidian
Obsidian (Volcanic Glass) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Amorphous (Non-crystalline) with a massive habit and characteristic conchoidal fracture
Mineral Group
Silicates (Extrusive Igneous Rock / Volcanic Glass)
Chemical Formula
SiO2 (approx. 70–75%) with MgO and Fe3O4 inclusions
Formation Process
Igneous (Volcanic). Formed by the rapid cooling of silica-rich (rhyolitic) lava, preventing crystal growth
About This Crystal
Deep black, opaque to translucent at edges, vitreous (glassy) luster with smooth, curved fracture surfaces
Physical Characteristics
Color: Black; Streak: White; Cleavage: None; Fracture: Conchoidal; SG: 2.35–2.6; Tenacity: Brittle; Fluorescence: Generally inert
Optical Properties
Refractive Index: 1.48–1.51; Single Refraction (Isotropic); Pleochroism: None; Luster: Vitreous
Hardness & Durability
Origin Region
Volcanically active regions including Mexico, USA (Oregon, California), Iceland, Japan, and Italy (Lipari)
Hardness & Durability
Mohs Hardness: 5 to 5.5. Brittle toughness; sensitive to scratches and impact; good for jewelry with low-impact settings
Care & Maintenance
Avoid ultrasonic cleaners and harsh chemicals; clean with warm soapy water and soft cloth; store separately from harder gems like quartz
Rarity & Value
Common. Value depends on size, polish, and special lusters (e.g., Rainbow or Gold Sheen); rarely treated or enhanced
Special Characteristics
Conchoidal fracture produces extremely sharp edges; can occasionally exhibit sheen, rainbow colors, or snowflake inclusions
Lore & History
Used since prehistoric times for arrowheads and ritual knives (Aztecs, Mayans); traditionally associated with grounding and protection