igneous
Weathered basalt (likely)
Basalt; fine-grained mafic volcanic rock, mainly plagioclase and pyroxene with possible olivine
AI-generated identification · may be incorrectDark gray-green, dull to faintly matte, fine-grained and rounded by weathering; typically Mohs 5–6, with no visible cleavage and an interlocking crystalline texture. The green tint may reflect chlorite or other alteration minerals.
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Physical properties
Dark gray-green, dull to faintly matte, fine-grained and rounded by weathering; typically Mohs 5–6, with no visible cleavage and an interlocking crystalline texture. The green tint may reflect chlorite or other alteration minerals.
Formation & geological history
Formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes; the specimen’s rounded shape indicates erosion or stream/beach transport.
Uses & applications
Used as crushed aggregate, road base, riprap, concrete material, and occasionally decorative stone; ordinary hand specimens have minimal commercial value.
Geological facts
Basalt is the most widespread volcanic rock on Earth and forms much of the oceanic crust, including seafloor pillow lavas.
Field identification & locations
Identify by its dense, fine texture, dark color, and lack of obvious quartz or large crystals; common in volcanic regions, river gravels, and glacial deposits. Exact identification would benefit from a fresh surface, streak, magnetism, and density tests.
