igneous
Rounded gray pebble, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; likely basalt (plagioclase ± pyroxene, possibly olivine)
AI-generated identification · may be incorrectGray, dull to weakly satin luster, fine-grained and rounded by abrasion; estimated Mohs hardness 5–6, with no obvious cleavage or visible crystals. Specific gravity is approximately 2.7–3.1 if basaltic.
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Physical properties
Gray, dull to weakly satin luster, fine-grained and rounded by abrasion; estimated Mohs hardness 5–6, with no obvious cleavage or visible crystals. Specific gravity is approximately 2.7–3.1 if basaltic.
Formation & geological history
Probably a weathered stream, beach, or glacial pebble eroded from volcanic rock; its exact geological age and formation locality cannot be determined from the photograph.
Uses & applications
Common basalt is used as crushed aggregate, road stone, ballast, and occasionally decorative stone; this small specimen has little commercial value.
Geological facts
Basalt is the most widespread volcanic rock on Earth and commonly forms from rapidly cooled lava, especially at oceanic spreading centers and hotspots.
Field identification & locations
Identify by its fine texture, dark gray color, high density, and absence of large crystals; a streak test, magnetism test, and close inspection for vesicles would help distinguish basalt from andesite or other pebbles. Common worldwide.
