igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Dark grey, black, or dark brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Basalts are found on every continent and make up most of the ocean floor.
Uses & applications
Used primarily as crushed stone for road base, railroad ballast, and concrete aggregate. It is also used in high-performance fibers and as a building stone (dimension stone).
Geological facts
Basalt is the most common volcanic rock on Earth. It also covers large areas of the Moon (the Lunar Maria), Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals to the naked eye. Commonly found in volcanic fields and oceanic crust outcrops.
