igneous
Basalt
Basalt
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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. Most basalt in this smooth form originates from volcanic activity and is later weathered by water.
Uses & applications
Used primarily in construction (crushed stone, concrete aggregate, asphalt pavement), decorative landscaping, and occasionally for stonework or 'hot stone' massage therapy due to heat retention.
Geological facts
Basalt is the most common rock on Earth's surface and also covers massive areas of the Moon's surface (the lunar maria). It is the primary rock type of the ocean floor.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions or as rounded cobbles in riverbeds and coastal areas.
