igneous
Polished black star-shaped stone, likely black obsidian
Obsidian (volcanic glass), primarily SiO₂
AI-generated identification · may be incorrectTypically black to dark gray, vitreous/glassy luster, hardness about 5–5.5 Mohs, no crystal structure or cleavage, conchoidal fracture, and specific gravity around 2.35–2.65. The smooth carved surface and star shape indicate human processing; the image alone cannot exclude black glass, basalt, or dyed stone.
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Physical properties
Typically black to dark gray, vitreous/glassy luster, hardness about 5–5.5 Mohs, no crystal structure or cleavage, conchoidal fracture, and specific gravity around 2.35–2.65. The smooth carved surface and star shape indicate human processing; the image alone cannot exclude black glass, basalt, or dyed stone.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystal growth, generally during Quaternary to recent volcanic activity. Major sources include Mexico, the western United States, Armenia, Turkey, and Japan.
Uses & applications
Used for ornamental carvings, cabochons, jewelry, knives, and collectibles; it has little industrial or construction value in this shaped form.
Geological facts
Obsidian is a natural glass rather than a true crystalline mineral. Sharp fresh edges can be extremely keen, historically enabling blades and projectile points.
Field identification & locations
Look for uniform glassy luster, conchoidal fractures, and absence of visible grains; a scratch test and examination for bubbles can help distinguish it from manufactured glass. Black obsidian is common and widely sold in lapidary shops.
