igneous
Likely basaltic rock
Fine- to medium-grained mafic igneous rock, probably basalt or metamorphosed basalt (metabasalt)
AI-generated identification · may be incorrectDark gray-green, dull to subtly crystalline, dense, and irregularly massive; likely hardness 5–6, with plagioclase and pyroxene ± olivine, and possible chlorite/epidote alteration. No clear cleavage or diagnostic crystal faces are visible.
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Physical properties
Dark gray-green, dull to subtly crystalline, dense, and irregularly massive; likely hardness 5–6, with plagioclase and pyroxene ± olivine, and possible chlorite/epidote alteration. No clear cleavage or diagnostic crystal faces are visible.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows or oceanic crust; if metamorphosed, it may be much older than the original lava. Age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally dimension stone; this small specimen has mainly educational or collectible value.
Geological facts
Basalt is the most abundant volcanic rock and forms much of the ocean floor. Greenish tones commonly indicate secondary minerals produced by low-grade alteration.
Field identification & locations
Look for a dark, heavy, fine-grained texture and possible tiny pale plagioclase crystals; a streak, magnetism, density, and thin-section examination would help distinguish basalt from metabasalt, gabbro, or slag. Common worldwide, especially oceanic islands, volcanic fields, and ancient greenstone belts.
