igneous
Polished dark stone sphere, likely black obsidian
Obsidian (natural volcanic glass; composition varies, commonly rhyolitic)
AI-generated identification · may be incorrectThe small, glossy, nearly black sphere appears opaque and polished. Obsidian has Mohs hardness about 5–5.5 and no crystal structure or cleavage; the image alone cannot confirm the material.
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Physical properties
The small, glossy, nearly black sphere appears opaque and polished. Obsidian has Mohs hardness about 5–5.5 and no crystal structure or cleavage; the image alone cannot confirm the material.
Formation & geological history
Obsidian forms when silica-rich lava cools rapidly, preventing crystals from growing. It is generally geologically young and occurs around volcanic vents and lava flows.
Uses & applications
Used for decorative spheres, jewelry, and carvings; historically, sharp-edged obsidian was fashioned into tools and blades.
Geological facts
Unlike most igneous rocks, obsidian is volcanic glass rather than a mass of visible mineral crystals.
Field identification & locations
A glassy luster and curved, shell-like fracture surfaces are clues, but a polished sphere is difficult to identify visually and could be another black stone. Obsidian occurs in volcanic regions worldwide, including the western United States, Mexico, and Iceland.
