igneous
Basalt pebble
Fine- to medium-grained mafic volcanic rock, chiefly plagioclase and pyroxene with possible olivine and iron oxides
AI-generated identification · may be incorrectHardness about 5–6 Mohs; dark brown to black, weathered surface, dull to slightly vitreous luster, dense and fine-grained, with no visible cleavage. The pale sparkling patches may be weathering products or small mineral-filled vesicles.
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Physical properties
Hardness about 5–6 Mohs; dark brown to black, weathered surface, dull to slightly vitreous luster, dense and fine-grained, with no visible cleavage. The pale sparkling patches may be weathering products or small mineral-filled vesicles.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic fields; specimens may range from ancient to geologically recent. This rounded piece was likely shaped by stream or beach abrasion.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, riprap, and landscaping stone; attractive polished pieces are sold as inexpensive specimens. Typical collector value is low.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and iron-rich oxides.
Field identification & locations
Identify by its heavy, dark, fine-grained texture, lack of obvious layering, and resistance to scratching; a hand lens can reveal tiny plagioclase crystals. Common worldwide, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic volcanic terrains.
