igneous
Basalt
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 6 (Mohs); Color: dark gray, black, or dark greenish-gray; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic), often contains micro-crystals of plagioclase feldspar and pyroxene; Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs)
- Color
- dark gray, black, or dark greenish-gray
- Luster
- dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: dark gray, black, or dark greenish-gray; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic), often contains micro-crystals of plagioclase feldspar and pyroxene; Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Basalts can range in age from modern volcanic eruptions to billions of years old.
Uses & applications
Primarily used as an aggregate in construction projects, such as road base, railroad ballast, and concrete. It is also used as a dimension stone for flooring and monuments.
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 extremely common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size (high density), and lack of visible individual crystals to the naked eye. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
