igneous
Rounded dark river pebble
Likely basalt or fine-grained mafic volcanic rock
AI-generated identification · may be incorrectDark gray to black, dull to faintly waxy luster, fine-grained and massive, with no visible crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1. The smooth rounded shape indicates natural water abrasion or tumbling.
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Physical properties
Dark gray to black, dull to faintly waxy luster, fine-grained and massive, with no visible crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.8–3.1. The smooth rounded shape indicates natural water abrasion or tumbling.
Formation & geological history
Probably weathered from a basaltic lava flow and transported in a river, beach, or glacial deposit; basalt commonly formed during the Cenozoic or older volcanic episodes. Exact identification requires a fresh surface or testing.
Uses & applications
Used as landscaping stone, aggregate, road material, garden rock, and occasionally as a decorative or craft stone; not typically suitable for jewelry-grade cutting.
Geological facts
Basalt is rich in plagioclase and pyroxene, commonly with minor olivine and magnetite. Its dark color reflects abundant iron- and magnesium-bearing minerals.
Field identification & locations
Look for uniform dark color, fine texture, heavy feel, and possible tiny feldspar crystals; a streak test, hardness test, magnetism check, and acid test can help distinguish basalt from slag, chert, or andesite. Common worldwide in volcanic regions and stream gravels.
