igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), typically containing plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), typically containing plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); 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. It can be found in oceanic crust, volcanic islands, and oceanic plateaus.
Uses & applications
Used primarily in construction for road base, concrete aggregate, and railroad ballast. It is also used in the manufacturing of stone wool (rock wool) insulation.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the Moon's lunar maria. Large regions of basalt are known as Flood Basalt Provinces, such as the Deccan Traps in India.
Field identification & locations
Identify in the field by its dark color, heavy weight (high density), and fine-grained texture. It often shows columnar jointing when found in large outcrops. It is common on coastlines and near active or extinct volcanoes.
