igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown or green; Luster: Dull to sub-vitreous; Texture: Fine-grained (aphanitic); Composition: Primarily plagioclase feldspar and pyroxene.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black, weathering to brown or green
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown or green; Luster: Dull to sub-vitreous; Texture: Fine-grained (aphanitic); Composition: Primarily plagioclase feldspar and pyroxene.
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 a moon. Most common rock on Earth's crust, forming the oceanic floor.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Also used for high-quality floor tiles and as a raw material for stone wool insulation.
Geological facts
Basalt makes up most of the ocean floor and is found on the Moon and Mars. When cooling, it often forms distinct hexagonal columns, such as those at the Giant's Causeway in Ireland.
Field identification & locations
Identify by its dark color, heavy weight (high density), and fine grain. Often found near volcanic activity or coastal areas as weathered cobbles. Look for small holes called vesicles formed by gas bubbles.
