igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or glassy; 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: fine-grained (aphanitic) or glassy; 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 moon. Most of Earth's ocean floor is basalt.
Uses & applications
Extensively used in construction, especially as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used for stone massage or aquarium decor.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also found on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and lack of visible crystals. Commonly found in volcanic regions and along oceanic ridges.
