Black Obsidian
Obsidian (Volcanic Glass) · Semi-Precious Gemstone / Mineraloid
Crystal System
Amorphous (Non-crystalline); lacks an internal atomic structure
Mineral Group
Amorphous Igneous Rock (Mineraloid)
Chemical Formula
SiO2 (70–75%) with MgO, Fe3O4 trace elements
Formation Process
Extrusive Igneous; formed when felsic lava cools so rapidly that crystal growth is impossible
About This Crystal
Jet-black, opaque to slightly translucent at thin edges, featuring a high vitreous (glassy) luster and smooth surface when polished into a crescent moon shape
Physical Characteristics
Color: jet black; Streak: white; Cleavage: none; Fracture: conchoidal (shell-like curves); Specific Gravity: 2.35–2.6; Luster: vitreous; Magnetism: weak due to magnetite inclusions
Optical Properties
Isotropic (Singly refractive); RI: 1.48–1.51; non-pleochroic; exhibit no birefringence; no fire; lacks play of color
Hardness & Durability
Origin Region
Mexico (notably Jalisco), USA (Oregon), Iceland, Japan; found in geologically recent volcanic areas
Hardness & Durability
Mohs hardness: 5.0–5.5; Brittle tenacity; sensitive to hard impacts and scratching from common household dust (quartz)
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic or steam cleaners; store separately from harder gems like quartz or beryl to prevent scratches
Rarity & Value
Common and abundant; inexpensive; price influenced primarily by carving craftsmanship; often sold as polished decorative objects or beads
Special Characteristics
Strong conchoidal fracture produces extremely sharp edges; can sometimes show 'Sheen' (Gold/Silver) or 'Rainbow' effects if microscopic gas bubbles or crystals are present, though this specimen appears solid black
Lore & History
Used by ancient civilizations for mirrors (Aztecs) and sharp weapons/surgical tools; traditionally associated with the Root Chakra and believed in lore to be a stone of protection and grounding