Black Obsidian
Volcanic Glass (felsic composition) · Mineraloid / Semi-Precious Gemstone
Crystal System
Amorphous (Non-crystalline material / Mineraloid)
Mineral Group
Volcanic Glass (Silicate-rich)
Chemical Formula
SiO2 (approx. 70-75%) + MgO, Fe3O4
Formation Process
Igneous: Forms from the rapid cooling of silica-rich (felsic) lava, preventing the growth of a crystalline lattice.
About This Crystal
A smooth, glassy stone with a deep black to dark grey hue. It exhibits a vitreous (glassy) luster and translucent edges when held to light. The surface shows characteristic conchoidal fracture scars.
Physical Characteristics
Color: jet black to smoky grey; Streak: white; Cleavage: none; Fracture: conchoidal (shell-like); Specific Gravity: 2.35-2.6; Tenacity: brittle; Fluorescence: typically inert.
Optical Properties
Refractive Index: 1.48-1.51; Isotropic (singly refractive); Lacks pleochroism or birefringence due to its amorphous nature.
Hardness & Durability
Origin Region
Volcanic regions worldwide; notably Mexico, Iceland, USA (Oregon/California), and Japan.
Hardness & Durability
Mohs hardness: 5.0 to 6.0; Brittle toughness; sensitive to scratches from quartz and harder minerals.
Care & Maintenance
Clean with warm soapy water and a soft cloth; avoid ultrasonic cleaners or harsh chemicals. Store separately to prevent scratching.
Rarity & Value
Common; value depends on size and unique sheen (e.g., Rainbow or Gold Sheen). Generally inexpensive as a specimen.
Special Characteristics
Displays conchoidal fracture (extremely sharp edges). Some varieties show 'sheen' from microscopic gas bubbles or inclusions, though this specimen appears to be basic black.
Lore & History
Used by ancient civilizations for surgical blades, arrowheads, and mirrors. Traditionally associated with protection and grounding in metaphysical lore.