igneous
Polished dark river stone, likely basalt
Fine-grained basalt; exact identification is uncertain from appearance alone
AI-generated identification · may be incorrectDark gray-brown, rounded and polished, with a mostly dull-to-slightly waxy luster and no visible crystals or cleavage. Basalt typically has Mohs hardness 5–6 and specific gravity about 2.8–3.0.
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Physical properties
Dark gray-brown, rounded and polished, with a mostly dull-to-slightly waxy luster and no visible crystals or cleavage. Basalt typically has Mohs hardness 5–6 and specific gravity about 2.8–3.0.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; basaltic rocks range from ancient to geologically recent. The smooth shape suggests abrasion during transport in water, followed by polishing.
Uses & applications
Commonly used as aggregate, road stone, and building stone; polished pieces are decorative or collectible.
Geological facts
Basalt is one of Earth’s most abundant volcanic rocks and also forms much of the ocean floor.
Field identification & locations
Look for a dense, fine-grained, dark rock without obvious layering; a fresh broken surface may show tiny crystals. Rounded stones occur in riverbeds and beaches; this specimen’s exact identity cannot be confirmed from the photo.
