igneous
Basalt Pebble
Basalt (Extrusive Mafic Igneous)
Hardness: 5-6 (Mohs), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0
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Physical properties
Hardness: 5-6 (Mohs), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded by fluvial or marine abrasion.
Uses & applications
Commonly used as construction aggregate, road base, concrete railroad ballast, and sometimes in stone massage therapy or landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Found globally on beaches, riverbeds, and volcanic regions.
