igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: dark grey to black or olive green; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- dark grey to black or olive green
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: dark grey to black or olive green; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most of Earth's basalt forms at mid-ocean ridges.
Uses & applications
Used extensively in construction as road base, railroad ballast, and aggregate in concrete; also used for high-end countertops or stone masonry.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the lunar maria on the Moon. It is the volcanic equivalent of gabbro.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and lack of visible individual mineral grains to the naked eye. Commonly found in volcanic regions and ocean floor crust.
