igneous
Basalt Pebble
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs), Color: Dark gray to black, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8-3.0
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Physical properties
Hardness: 6 (Mohs), Color: Dark gray to black, Luster: Dull/Matte, Crystal structure: Aphanitic (fine-grained), 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. These small pebbles are often smoothed by water erosion in riverbeds or coastal areas.
Uses & applications
Larger quantities are used in construction for aggregate and road base. This specific specimen is a common geological curiousity or yard stone.
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 common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible crystals to the naked eye. Found worldwide in volcanic regions and river deposits.
