igneous
Fine-grained volcanic rock, likely basalt
Basalt; predominantly plagioclase feldspar and pyroxene, with possible olivine and iron-titanium oxides
AI-generated identification · may be incorrectDark gray-green, dull to faintly granular, and apparently massive with no visible crystals; typical basalt hardness is about 5–6 Mohs and specific gravity 2.8–3.0. The rounded edges may reflect weathering or abrasion.
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Physical properties
Dark gray-green, dull to faintly granular, and apparently massive with no visible crystals; typical basalt hardness is about 5–6 Mohs and specific gravity 2.8–3.0. The rounded edges may reflect weathering or abrasion.
Formation & geological history
Basalt forms when low-viscosity mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields, oceanic crust, and flood-basalt provinces. Its exact age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, concrete aggregate, and building stone; attractive polished pieces may be collected, though this specimen appears ordinary.
Geological facts
Its greenish tone may result from weathering or alteration minerals such as chlorite, epidote, or clay. The image does not show diagnostic crystals, vesicles, or layering, so a precise identification is limited.
Field identification & locations
Look for a dense, fine-grained texture, dark color, and lack of obvious layering; a streak, magnetism, acid test, and fresh broken surface would help distinguish basalt from greenstone, concrete, or other dark rocks. Common worldwide, especially volcanic regions and river gravels.
