igneous
Rounded dark river stone
Likely basalt or fine-grained andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to faintly satin luster, smoothly water-worn and oval. Likely hardness about 5–6 Mohs, with no visible cleavage; specific gravity commonly 2.7–3.1.
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Physical properties
Dark gray-green, fine-grained, dull to faintly satin luster, smoothly water-worn and oval. Likely hardness about 5–6 Mohs, with no visible cleavage; specific gravity commonly 2.7–3.1.
Formation & geological history
Probably a glacially or fluvially transported volcanic rock, rounded by abrasion; its precise geological age and source cannot be determined from the photograph.
Uses & applications
Used as a decorative stone, landscaping material, aquarium stone, or collectible; not typically valuable as a gem or construction stone in this form.
Geological facts
The fine texture suggests rapid cooling of lava at or near Earth’s surface. A streak, fresh broken surface, magnet test, and close inspection for crystals would help distinguish basalt from andesite or other dark rocks.
Field identification & locations
Common in river gravels, beaches, glacial deposits, and volcanic regions worldwide. Basalt is usually dense, non-foliated, and may contain tiny plagioclase or pyroxene crystals; avoid assuming identity from color alone.
