igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to slightly metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to slightly metallic
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to slightly metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
Formation & geological history
Basalt forms from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is a volcanic rock often found in oceanic crust and huge flood basalt provinces.
Uses & applications
Extensively used in construction for crushed stone, road base, concrete aggregate, and railroad ballast. Also used as a primary material in stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It also makes up the lunar maria on the Moon and much of the surface of Mars and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often shows vesiculation (small holes) if gas was trapped, though this specimen is solid.
