igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale). Color: Dark grey to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine or pyroxene.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale). Color: Dark grey to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), often containing phenocrysts of olivine or pyroxene.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic magma) exposed at or very near the Earth's surface. Common in oceanic crust and shield volcanoes.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and dimension stone for buildings.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up a large portion of the crust on the Moon and Mars (specifically the lunar maria).
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and very fine-grained texture. It often breaks with a conchoidal or irregular fracture. Found globally, especially in volcanic regions like Hawaii or the Pacific Northwest.
