igneous
Red-brown river cobble, likely weathered basalt
Basalt; fine-grained mafic rock composed mainly of plagioclase and pyroxene, commonly with iron oxides
AI-generated identification · may be incorrectDark reddish-brown, dull to faintly subvitreous luster, rounded by abrasion, and apparently fine-grained with no visible crystals; typical hardness is about 6 Mohs and specific gravity 2.8–3.0. The red color likely reflects oxidation of iron-bearing minerals.
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Physical properties
Dark reddish-brown, dull to faintly subvitreous luster, rounded by abrasion, and apparently fine-grained with no visible crystals; typical hardness is about 6 Mohs and specific gravity 2.8–3.0. The red color likely reflects oxidation of iron-bearing minerals.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. The specimen’s smooth shape indicates prolonged transport in a river or beach environment; its exact age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road base, riprap, concrete aggregate, and landscaping stone; attractive polished pieces may be sold as decorative or lapidary material.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly weathers to reddish iron-oxide coatings or soil. Similar-looking red jasper, andesite, or ironstone cannot be excluded from a photograph alone.
Field identification & locations
Look for a dense, uniform fine-grained texture, high weight, lack of obvious layering, and weak attraction or no attraction to a magnet; a streak, fresh fracture, and hand lens would improve identification. Common sources include volcanic terrains and gravel beds worldwide.
