igneous
Basalt Pebble
Basalt (Mafic volcanic rock)
Hardness: 6-7 (Mohs scale), Color: Dark grey to black, Luster: Dull/earthy, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8–3.0.
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to black, Luster: Dull/earthy, 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 surface of Earth. This specimen appears water-worn, likely from a river or beach environment.
Uses & applications
Used widely in construction for aggregate, road base, and railroad ballast. Small polished pebbles are used in landscaping and aquarium decor.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight (density), dark color, and fine-grained texture. It often shows small pits or vesicles if gas was trapped during cooling. Found worldwide in volcanic provinces.
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