igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale; dark gray to black color; dull to sub-aphanitic luster; microcrystalline or aphanitic structure; 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-aphanitic luster; microcrystalline or aphanitic 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 surface of a planet or moon, often smoothed by wave action in marine environments.
Uses & applications
Used in construction, as aggregate in concrete, road base, and historically for cobblestones and building stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans. Similar rocks are also found extensively on the Moon and Mars.
Field identification & locations
Found worldwide along beaches, riverbeds, and volcanic regions. Identified by its dark, fine-grained appearance, heavy weight relative to size, and smooth water-worn shape.
