igneous
Polished basalt pebble
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectHardness about 6–7 Mohs; dark brown to black, fine-grained, and commonly dull to glassy when polished. It has an interlocking microscopic crystal structure, no visible cleavage, and specific gravity roughly 2.8–3.1.
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Physical properties
Hardness about 6–7 Mohs; dark brown to black, fine-grained, and commonly dull to glassy when polished. It has an interlocking microscopic crystal structure, no visible cleavage, and specific gravity roughly 2.8–3.1.
Formation & geological history
Basalt is an extrusive igneous rock formed when low-viscosity mafic lava cools rapidly at or near Earth’s surface, commonly during volcanic eruptions; its age depends on locality and may range from recent to billions of years.
Uses & applications
Used as aggregate, road stone, paving, building stone, and occasionally as a polished ornamental or worry stone; this shaped specimen is primarily decorative or collectible.
Geological facts
The rounded form and glossy surface indicate natural water abrasion followed by polishing or tumbling. Small pale or metallic-looking patches may represent altered minerals, vesicle fillings, or weathering products.
Field identification & locations
Identify it by its heavy feel, dark fine-grained appearance, lack of obvious large crystals, and resistance to scratching by steel; basalt commonly occurs in volcanic regions, river gravels, and oceanic crust.
