igneous
Rounded gray river pebble, likely basaltic rock
Fine-grained basalt or andesite; exact identification requires a hand specimen or thin section
AI-generated identification · may be incorrectDark gray, dull to weakly silky, fine-grained and massive, with no obvious cleavage; typical hardness about 5–6 Mohs and specific gravity roughly 2.7–3.1. Its smooth, rounded shape indicates prolonged water abrasion.
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Physical properties
Dark gray, dull to weakly silky, fine-grained and massive, with no obvious cleavage; typical hardness about 5–6 Mohs and specific gravity roughly 2.7–3.1. Its smooth, rounded shape indicates prolonged water abrasion.
Formation & geological history
Likely an extrusive volcanic rock formed when basaltic-to-intermediate lava cooled rapidly at or near Earth’s surface, probably millions to billions of years ago depending on locality. Later erosion and stream transport rounded it.
Uses & applications
Common basalt is used for crushed aggregate, road base, riprap, paving, and landscaping; attractive polished pieces are sold as decorative stones. This specimen has little commercial value unless provenance or unusual texture is established.
Geological facts
Basalt commonly contains plagioclase feldspar, pyroxene, and often olivine or iron oxides. The visible pale speckling may represent feldspar or weathered mineral grains.
Field identification & locations
Look for a dense, fine texture, dark gray color, lack of visible large crystals, and possible weak attraction to a magnet from iron-bearing minerals. Common sources include volcanic terrains and gravel bars worldwide.
