igneous
Rounded gray-green pebble, likely basalt or fine-grained metamorphic rock
Probable basalt (plagioclase–pyroxene–iron oxide aggregate); exact identification requires testing
AI-generated identification · may be incorrectHardness about 5.5–6.5 Mohs; dark gray to greenish gray, dull to faintly granular luster, very fine-grained and massive, with no visible cleavage. The smooth rounded form indicates water or abrasion polishing.
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Physical properties
Hardness about 5.5–6.5 Mohs; dark gray to greenish gray, dull to faintly granular luster, very fine-grained and massive, with no visible cleavage. The smooth rounded form indicates water or abrasion polishing.
Formation & geological history
Most consistent with an eroded volcanic basalt formed by cooling of mafic lava, generally millions to billions of years old depending on its source; it may also be a metamorphosed equivalent such as greenstone.
Uses & applications
Commonly used as aggregate, road stone, riprap, and decorative landscaping material; this small rounded specimen has modest collecting value.
Geological facts
Basalt is the most widespread volcanic rock on Earth and forms much of the oceanic crust. Its iron- and magnesium-rich minerals commonly weather to greenish or brown surfaces.
Field identification & locations
Look for a dense, fine-grained texture, dark color, and lack of visible quartz; it should not fizz with dilute hydrochloric acid and may scratch glass. Common in stream beds, beaches, glacial deposits, and volcanic regions.
