igneous
Polished black obsidian pyramid/block
Obsidian — natural volcanic glass, chiefly rhyolitic silica (approximately 70–75% SiO₂)
AI-generated identification · may be incorrectUsually glossy black with conchoidal fracture, no visible crystals, Mohs hardness about 5–5.5, vitreous luster, and no cleavage; this specimen is cut and polished into a geometric form. Surface scratches and reflections are visible, and the sharp edges are typical of glassy material.
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Physical properties
Usually glossy black with conchoidal fracture, no visible crystals, Mohs hardness about 5–5.5, vitreous luster, and no cleavage; this specimen is cut and polished into a geometric form. Surface scratches and reflections are visible, and the sharp edges are typical of glassy material.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow, generally during relatively young volcanic eruptions from the Cenozoic to present. Common sources include Mexico, the western United States, Armenia, Iceland, and Japan.
Uses & applications
Used for ornamental carvings, pyramids, cabochons, jewelry, and historically extremely sharp tools and projectile points. This appears primarily decorative or collectible.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks an ordered crystal structure. Black color commonly results from microscopic iron-bearing minerals or inclusions.
Field identification & locations
Identify by its glassy luster, uniform dark color, sharp edges, and curved conchoidal fracture; unlike manufactured glass, natural obsidian may show flow bands or tiny inclusions. A scratch, refractive-index, or professional examination can distinguish it from black glass or dyed stone.
