igneous
Basalt
Extrusive Mafic Igneous Rock
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/Earthly, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Fragmental, Specific gravity: 2.9-3.1
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark gray to black, Luster: Dull/Earthly, Crystal structure: Aphanitic (fine-grained), Cleavage: None/Fragmental, Specific gravity: 2.9-3.1
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Found in oceanic crust, volcanic islands, and flood basalt provinces.
Uses & applications
Extensively used in construction, road base, concrete aggregate, railroad ballast, and ground for high-quality insulation (stone wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and almost the entirety of the ocean floor is composed of it. It is also common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture lacking visible crystals without a lens. Found globally in volcanic regions.
