igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-vitreous luster, fine-grained aphanitic crystal structure, no prominent cleavage, specific gravity around 2.8 - 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-vitreous luster, fine-grained aphanitic crystal structure, no prominent cleavage, 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. Geologically widespread, dating from ancient Precambrian times to modern volcanic events.
Uses & applications
Used in construction as crushed stone, aggregate in concrete, railroad ballast, and in the manufacturing of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust beneath the oceans and makes up most of the oceanic crust. It is also found extensively on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained appearance and smooth, water-worn shape when found as a pebble on beaches or riverbeds. Common worldwide.
