igneous
Basalt (Road Aggregate)
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark gray to charcoal black; Luster: Dull/Earthy; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8 - 3.0. This specimen appears weathered/rounded with a slight sheen.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to charcoal black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to charcoal black; Luster: Dull/Earthy; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8 - 3.0. This specimen appears weathered/rounded with a slight sheen.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface (extrusive). Most common in oceanic crust and volcanic regions.
Uses & applications
Predominantly used as crushed stone aggregate for road construction, railroad ballast, and concrete production due to its durability and compressive strength.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found in abundance on the Moon and Mars (the dark 'seas' or Maria on the Moon are basaltic plains).
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Commonly found in gravel driveways, near railroad tracks, or in areas with volcanic history.
