igneous
Fine-grained gray igneous rock, likely basalt
Basalt; primarily plagioclase feldspar and pyroxene, commonly with olivine and iron-titanium oxides
AI-generated identification · may be incorrectDark gray, dull to faintly vitreous, very fine-grained and massive; hardness about 6–7 Mohs, poor cleavage as a whole, and typical specific gravity 2.8–3.0. The rounded shape appears water-worn rather than naturally crystalline.
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Physical properties
Dark gray, dull to faintly vitreous, very fine-grained and massive; hardness about 6–7 Mohs, poor cleavage as a whole, and typical specific gravity 2.8–3.0. The rounded shape appears water-worn rather than naturally crystalline.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows and oceanic crust; specimens may range from geologically ancient to recent. The image alone cannot establish its exact age or locality.
Uses & applications
Used as crushed aggregate, road base, railway ballast, riprap, building stone, and occasionally decorative pavers or polished objects; generally low jewelry value.
Geological facts
Its fine texture indicates rapid cooling, preventing large crystals from developing. Vesicles, if present, may later fill with zeolites, calcite, or quartz.
Field identification & locations
Look for a dense dark-gray body, tiny interlocking crystals, and occasional vesicles; a streak test is usually gray, and it commonly does not fizz with dilute hydrochloric acid. Common worldwide, especially volcanic regions and oceanic shorelines.
