igneous
Basalt (with possible fluidal texture)
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 5-6 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) with visible flow texture or lineation; Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) with visible flow texture or lineation; 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 surface of a planet or moon. This specimen shows linear surface features likely representing flow lines or cooling fractures.
Uses & applications
Used extensively in construction as aggregate, road base, and railroad ballast. Fine specimens are used in stone masonry and for making 'hot stones' for massage therapy.
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 on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Look for it in volcanic regions, along coastal areas near basaltic flows, or in glacial till.
