igneous
Basalt Pebble
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8 to 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8 to 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 erosion.
Uses & applications
Used in construction as crushed stone, road base, or concrete aggregate. Polished versions are used in hot stone massage and decorative 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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible crystals. Commonly found on volcanic beaches, riverbeds near volcanic activity, and oceanic islands like Hawaii.
