igneous
Mahogany obsidian crystal point
Volcanic glass, primarily rhyolitic silica (SiO₂), with iron-oxide inclusions
AI-generated identification · may be incorrectMohs hardness about 5–5.5; black to dark brown with reddish-brown mahogany patches, vitreous luster, amorphous (noncrystalline) structure, and conchoidal fracture; no cleavage. The polished, faceted point is human-shaped.
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Physical properties
Mohs hardness about 5–5.5; black to dark brown with reddish-brown mahogany patches, vitreous luster, amorphous (noncrystalline) structure, and conchoidal fracture; no cleavage. The polished, faceted point is human-shaped.
Formation & geological history
Forms when silica-rich lava cools rapidly, preventing crystal growth; mahogany coloration comes from dispersed hematite or magnetite. Usually Quaternary to younger volcanic material, especially from volcanic regions of the western United States.
Uses & applications
Used for ornamental carvings, cabochons, crystal points, jewelry, and lapidary décor; historically, obsidian was knapped into exceptionally sharp tools and weapons.
Geological facts
Obsidian is technically a natural glass rather than a true crystalline mineral. Its sharp conchoidal edges can be sharper than surgical steel, though it is brittle.
Field identification & locations
Identify by its glassy luster, opaque black-brown color, reddish iron-rich patches, light weight relative to many dark rocks, and curved fracture surfaces. Common sources include Oregon, Utah, Arizona, Mexico, and Armenia.
