igneous
Basalt
Mafic Igneous Rock (composed of plagioclase feldspar and pyroxene)
Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to rust-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black, weathering to rust-brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to rust-brown; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) at the Earth's surface or on the ocean floor. Most basaltic formations date from various Cenozoic volcanic events to the present day.
Uses & applications
Extensively used in construction as an aggregate for road bases and concrete. In industry, it is melted to create stone wool insulation. Also used as floor tiles and for landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust, covering most of the ocean floor. The dark patches on the Moon (the Lunar Maria) are also composed of basaltic lava flows.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and very fine grain where individual crystals are not visible to the naked eye. Often exhibits 'desert varnish' or a pitted texture if weathered. Commonly found in volcanic regions and along oceanic ridges.
