igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to vitreous; Crystal structure: Microcrystalline/Aphanitic; Cleavage: None; Specific gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to vitreous
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to vitreous; Crystal structure: Microcrystalline/Aphanitic; Cleavage: None; 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 Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction as aggregate for roads, railroad ballast, and concrete. It can also be melted into fibers for insulation (basalt wool).
Geological facts
Basalt is the most common rock on Earth's surface, making up most of the ocean floor and the lunar maria on the Moon.
Field identification & locations
Identify in the field by its dark color, fine grain (crystals invisible to the naked eye), and high density relative to other common stones. Usually found in volcanic fields.
