igneous
Basalt Pebble
Aphanitic Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to brownish-black color, dull to sub-metamorphic luster, fine-grained (aphanitic) crystal structure, specific gravity around 2.8-3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to brownish-black color, dull to sub-metamorphic luster, fine-grained (aphanitic) crystal structure, specific gravity around 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the Earth's surface.
Uses & applications
Used in construction, as aggregate in road building, railroad ballast, and occasionally for decorative landscaping or polished stones.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the oceans, and is also found abundantly on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained appearance and heavy feel. Often found smoothed and rounded along riverbeds and ocean beaches due to wave action.
