igneous
Basalt
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic, Crystal 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, Crystal 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 Earth's surface. Most basalt is Cenozoic in age but can range back to the Archean.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and as a decorative stone or architectural material.
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 on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Commonly found in volcanic fields, oceanic islands, and mid-ocean ridges.
