igneous
Basalt (Weathered River Pebble)
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark grey to black color with brownish weathering rinds, dull to sub-metamorphic luster, aphanitic (fine-grained) crystal structure, specific gravity around 2.8 - 3.0
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Physical properties
Hardness of 6 on the Mohs scale, dark grey to black color with brownish weathering rinds, dull to sub-metamorphic luster, aphanitic (fine-grained) 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 the surface of a planet or moon, often subsequently weathered and rounded by water transport in a river bed over thousands to millions of years
Uses & applications
Used in construction, aggregate, road base, and landscape stone; collected by hobbyists as river rocks
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and it is also commonly found on the Moon and Mars
Field identification & locations
Easily identified by its dark, heavy, fine-grained nature and smooth, water-worn texture when found in riverbeds
