igneous
Basalt Pebble
Aphanitic extrusive igneous rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-vetreous 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 black color, dull to sub-vetreous 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. Water-worn into a pebble shape in a river or beach environment.
Uses & applications
Used in construction, road aggregate, railroad ballast, and landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins, and is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy feel relative to its size, and fine-grained texture. Commonly found in riverbeds, beaches, and volcanic regions worldwide.
