igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; Luster: Dull/earthy; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often weathering to brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brown; 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 near the surface of a planet or moon. It is the most common volcanic rock on Earth, covering much of the ocean floors.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and concrete. It is also used as floor tiles, monuments, and 'hot stones' for massage due to its heat retention.
Geological facts
Basalt is found across the solar system; the dark regions of the Earth's Moon, known as maria, are huge plains of basaltic lava flows. It creates iconic columnar joints like the Giant's Causeway.
Field identification & locations
Identify by its heavy weight (density), dark color, and fine-grained texture lacking visible crystals. It is ubiquitous in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
