igneous
Basalt
Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); 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. It is the most common rock type in the Earth's crust, making up most of the ocean floor.
Uses & applications
Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used in stone carving and architecture.
Geological facts
Basalt is found across the solar system; it makes up the 'maria' (dark plains) on the Moon and much of the surface of Mars and Venus.
Field identification & locations
Identify by its dark color, heavy weight for its size, and microscopic crystal structure. Often found near volcanic activity sites and coastal areas. Commonly used as 'river rocks' in landscaping.
