igneous
Polished black stone sphere, likely obsidian
Obsidian — naturally occurring volcanic glass, chiefly silica-rich rhyolitic glass
AI-generated identification · may be incorrectGlossy black, spherical and polished; obsidian has no crystal structure or cleavage and is typically Mohs 5–5.5. The photo does not show enough detail to confirm the material; other dark stones may look similar.
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Physical properties
Glossy black, spherical and polished; obsidian has no crystal structure or cleavage and is typically Mohs 5–5.5. The photo does not show enough detail to confirm the material; other dark stones may look similar.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals do not grow, commonly in volcanic flows and domes; its age depends on the source deposit.
Uses & applications
Polished spheres are used for decoration and collecting; obsidian is also made into jewelry and, historically, sharp-edged tools.
Geological facts
Obsidian breaks with a curved, shell-like fracture that can produce exceptionally sharp edges.
Field identification & locations
A glassy luster and conchoidal fracture help distinguish obsidian from crystalline rocks, but this polished sphere cannot be identified reliably from appearance alone. Obsidian occurs in volcanic regions worldwide, including Mexico, the western United States, Iceland, and Japan.
