igneous
Likely basalt or dark mafic rock fragment
Basalt; primarily plagioclase feldspar and pyroxene, commonly with olivine and iron oxides
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to slightly vitreous luster, with no visible cleavage; typical hardness is about 5–6 Mohs and specific gravity roughly 2.8–3.1. The specimen appears rough and possibly cut or broken, limiting confident identification from the image alone.
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Physical properties
Dark gray-green, fine-grained, dull to slightly vitreous luster, with no visible cleavage; typical hardness is about 5–6 Mohs and specific gravity roughly 2.8–3.1. The specimen appears rough and possibly cut or broken, limiting confident identification from the image alone.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic regions and oceanic crust; many examples range from recent to billions of years old. Its green coloration may reflect alteration to chlorite or other secondary minerals.
Uses & applications
Used as crushed aggregate, road base, railroad ballast, building stone, and occasionally as a lapidary or decorative material.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the oceanic crust.
Field identification & locations
Identify it by its dark, dense, fine-grained texture, lack of obvious quartz, and attraction only weakly or variably to a magnet; distinguish it from gabbro by its finer grain size. Common localities include Hawaii, Iceland, India’s Deccan Traps, and oceanic volcanic terrains.
