igneous
Tumbled dark stone, likely basalt
Basalt, chiefly plagioclase feldspar and pyroxene, with possible olivine and magnetite
AI-generated identification · may be incorrectDark gray-black, fine-grained, opaque, and weakly lustrous with a rounded, polished surface; Mohs hardness about 5–6, no visible cleavage, and typically specific gravity 2.8–3.1. The pits and irregular texture may reflect vesicles or weathering.
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Physical properties
Dark gray-black, fine-grained, opaque, and weakly lustrous with a rounded, polished surface; Mohs hardness about 5–6, no visible cleavage, and typically specific gravity 2.8–3.1. The pits and irregular texture may reflect vesicles or weathering.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Individual specimens may range from ancient Precambrian flows to geologically young lavas.
Uses & applications
Used widely as crushed aggregate, paving stone, construction rock, and occasionally as a decorative or polished stone. Common tumbled pieces have modest collecting value.
Geological facts
Its dark color and relatively high density distinguish it from many lighter volcanic rocks; magnetite-bearing basalt may show slight attraction to a strong magnet.
Field identification & locations
Common worldwide, especially in Hawaii, Iceland, the Columbia River Basalt Province, India’s Deccan Traps, and oceanic islands. Confirm with a fresh edge, hardness test, density, and magnet test; exact identification from the image is approximate.
