igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, dull to sub-vitreous luster, aphanitic (fine-grained) crystal structure, poor or absent cleavage, and 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, aphanitic (fine-grained) crystal structure, poor or absent cleavage, and 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, often shaped into a smooth pebble by water and sediment transport over thousands to millions of years.
Uses & applications
Used in construction, road aggregate, railroad ballast, and sometimes in landscaping or decorative stone.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and also makes up significant portions of the volcanic provinces on the Moon and Mars.
Field identification & locations
Easily identified by its dark, fine-grained matrix and heavy feel relative to its size. Commonly found in riverbeds, beaches, and volcanic regions worldwide.
