igneous
Rounded gray pebble, likely basalt or andesite
Fine-grained mafic volcanic rock; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to slightly waxy luster, massive texture, and no visible crystals or cleavage. Likely hardness about 5–6 Mohs and specific gravity roughly 2.7–3.0; its rounded shape and surface band reflect water abrasion or weathering.
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Physical properties
Dark gray-green, fine-grained, dull to slightly waxy luster, massive texture, and no visible crystals or cleavage. Likely hardness about 5–6 Mohs and specific gravity roughly 2.7–3.0; its rounded shape and surface band reflect water abrasion or weathering.
Formation & geological history
Probably formed when lava cooled rapidly at or near Earth’s surface, then was transported and rounded by a stream or beach. Its precise geological age and volcanic source cannot be determined from the photograph.
Uses & applications
Common basalt and andesite are used as aggregate, road stone, riprap, paving, and occasionally building stone; this small specimen has mainly educational or decorative value.
Geological facts
The prominent horizontal dark band may be a flow texture, weathering rind, or mineral-rich seam rather than a separate rock layer. A streak test, magnetism test, and fresh-surface examination would improve identification.
Field identification & locations
Look for a uniformly fine texture, absence of obvious quartz, and dark gray coloration; basalt is typically darker and denser than andesite. Common worldwide, especially in volcanic terrains and river gravels.
