igneous
Basalt
Basalt (Aphanitic Mafic Rock)
Hardness: 6 (Mohs); Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic), typically contains pyroxene and plagioclase feldspar; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic), typically contains pyroxene and plagioclase feldspar; Specific Gravity: 2.8–3.0
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. It is the most common volcanic rock on Earth, making up most of the ocean floor and large continental provinces.
Uses & applications
Used extensively in construction as an aggregate, road base, railroad ballast, and in the production of high-strength stone wool insulation. Also used in decor and as dimension stone.
Geological facts
Basalt is the primary rock type of the lunar maria on the Moon and covers vast areas of Mars and Venus. Giant's Causeway in Northern Ireland is a famous example of columnar basalt joints.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystal grains to the naked eye. Commonly found in volcanic regions and oceanic crustal exposures.
