igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic (if fresh); Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic (if fresh)
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic (if fresh); Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface of a planet or moon. It is the most common rock in Earth's crust, primarily making up the ocean floor.
Uses & applications
Extensively used in construction as aggregate for roads and concrete, railroad ballast, and for high-temperature insulation (stone wool).
Geological facts
Basalt is also found on the Moon and Mars, making up the vast plains known as lunar maria. Columnar basalt creates unique geometric pillars as the lava cools and contracts.
Field identification & locations
Identified in the field by its dark color, heavy weight for its size, and very fine grains that are usually not visible to the naked eye. Commonly found in volcanic regions and oceanic crustal outcrops.
