igneous
Dark rounded pebble, likely basalt or volcanic rock
Fine-grained mafic igneous rock; possibly basalt (composition chiefly plagioclase and pyroxene)
AI-generated identification · may be incorrectDark gray-brown, rounded and weathered, with a dull to weakly vitreous luster; likely hardness about 5–6 Mohs, dense, fine-grained, and lacking visible cleavage or crystals.
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Physical properties
Dark gray-brown, rounded and weathered, with a dull to weakly vitreous luster; likely hardness about 5–6 Mohs, dense, fine-grained, and lacking visible cleavage or crystals.
Formation & geological history
Likely formed when mafic lava cooled rapidly at or near Earth’s surface, then was rounded by stream, beach, or glacial transport. Basalt commonly ranges from Precambrian to recent age; age cannot be determined from the image.
Uses & applications
Common basalt is used as aggregate, road material, riprap, and building stone; attractive polished pieces may be collected, but this small specimen has minimal commercial value.
Geological facts
The image is insufficient for a definitive identification because grain size, streak, magnetism, and texture are not clearly visible.
Field identification & locations
Test for a gray-black streak, high density, and occasional weak magnetism; a hand lens may reveal tiny plagioclase crystals. Common worldwide, especially in volcanic regions and river or beach gravels.
