igneous
Basalt
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to earthy; Texture: fine-grained (aphanitic); Composition: high in pyroxene and plagioclase feldspar; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- dark gray to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to earthy; Texture: fine-grained (aphanitic); Composition: high in pyroxene and plagioclase feldspar; 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.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be used for thermal insulation in stone wool form.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large areas of India, the USA (Columbia River Plateau), and Brazil are covered by basaltic lava flows known as flood basalts.
Field identification & locations
Identify by its dark, heavy, and fine-grained appearance. It often breaks into sharp fragments. Typically found in volcanic regions or as glacial erratic stones in other areas.
