igneous
Weathered dark igneous rock, likely basalt
Basalt, predominantly plagioclase feldspar and pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectFine-grained, dark gray to greenish-black, dull to slightly vitreous luster, commonly massive with no visible cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.0. The specimen appears weathered and may contain lighter mineral grains or alteration patches.
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Physical properties
Fine-grained, dark gray to greenish-black, dull to slightly vitreous luster, commonly massive with no visible cleavage; Mohs hardness about 5–6 and specific gravity roughly 2.8–3.0. The specimen appears weathered and may contain lighter mineral grains or alteration patches.
Formation & geological history
Basalt forms when low-silica mafic lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic fields, and flood-basalt provinces. Most examples range from recent volcanic material to hundreds of millions of years old.
Uses & applications
Used as crushed aggregate, road metal, railway ballast, riprap, building stone, and occasionally as a decorative lapidary material; ordinary specimens have little jewelry value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. Vesicles, if present, indicate gas bubbles trapped during cooling, while green alteration may reflect weathering of olivine or pyroxene.
Field identification & locations
Identify it by its dark color, heavy feel, fine texture, and lack of obvious quartz; a streak test is typically gray, and a hand lens may reveal tiny feldspar crystals. Common worldwide, especially volcanic regions and beaches receiving basaltic material.
