igneous
Dark gray pebble, likely basalt
Basalt (fine-grained mafic volcanic rock; identification is tentative from the image)
AI-generated identification · may be incorrectOpaque, dark gray-brown, dull to slightly reflective, with rounded edges and no visible crystals. Basalt is typically made of plagioclase and pyroxene, has Mohs hardness about 6, and specific gravity around 2.8–3.0; crystal structure is too fine-grained to see.
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Physical properties
Opaque, dark gray-brown, dull to slightly reflective, with rounded edges and no visible crystals. Basalt is typically made of plagioclase and pyroxene, has Mohs hardness about 6, and specific gravity around 2.8–3.0; crystal structure is too fine-grained to see.
Formation & geological history
Forms when mafic lava cools rapidly at or near Earth’s surface. Basalt occurs from geologically recent eruptions to ancient volcanic terrains; the pebble’s age cannot be determined from the image.
Uses & applications
Basalt is used as crushed aggregate, road stone, and building material; this small pebble has little practical or jewelry use.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
Look for a dense, dark, fine-grained texture; confirm with a fresh broken surface, since several rocks and minerals can look similar. Basalt is common near volcanic regions and in river or beach gravels.
