Obsidian
Obsidian (Volcanic Glass) · Minor Gemstone / Mineral Specimen / Ornamental Stone
Crystal System
Amorphous (Non-crystalline material / Mineraloid)
Mineral Group
Silicates (Extrusive Igneous Rock / Volcanic Glass)
Chemical Formula
SiO2 (approx. 70–75%) with varying amounts of MgO and Fe3O4
Formation Process
Igneous: Forms when high-silica lava cools extremely rapidly (quenching), preventing the formation of a crystalline structure.
About This Crystal
A jet-black to dark grey, glass-like specimen with a highly reflective vitreous luster. It appears opaque in mass but can be translucent on thin edges. The surface shows characteristic smooth, curved conchoidal fracture faces.
Physical Characteristics
Color: Black; Streak: White; Cleavage: None; Fracture: Conchoidal (shell-like); Specific Gravity: 2.35–2.60; Tenacity: Brittle; Fluorescence: Typically inert.
Optical Properties
Refractive Index: 1.48–1.51 (Isotropic); Singly refractive; Exhibits high vitreous luster; no pleochroism due to amorphous structure.
Hardness & Durability
Origin Region
Volcanic regions worldwide including Mexico, USA (Oregon, California), Iceland, Japan, and Italy (Lipari).
Hardness & Durability
Mohs Hardness: 5 to 5.5. Brittle with poor toughness; easily scratched by steel and prone to chipping resulting in razor-sharp edges.
Care & Maintenance
Clean with warm soapy water and a soft cloth. Avoid ultrasonic cleaners and sudden temperature changes. Store separately to prevent scratches from harder gemstones like quartz.
Rarity & Value
Common; Value is generally low for rough specimens, though varieties like Rainbow or Fire Obsidian command higher prices. Common treatments are rare as it is abundant.
Special Characteristics
Displays perfect conchoidal fracture, producing edges thinner than surgical steel. Thin flakes may show slight transparency or brown-grey tints.
Lore & History
Historically used by ancient civilizations (Aztecs, Greeks) for mirrors, weapons, and surgical blades. Symbolically associated with protection, grounding, and the Root Chakra in contemporary lore.