igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Structure: Fine-grained/Aphanitic, Cleavage: None, Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Structure: Fine-grained/Aphanitic, 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 near the surface of a terrestrial planet or moon. Predominantly from volcanic activity over the last 4.5 billion years.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and ground-up for asphalt and concrete.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found in lava flows and oceanic crust.
