igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6-7 Mohs; Color: dark grey to black (weathered to brown); Luster: dull/earthy; Texture: fine-grained (aphanitic); Composition: plagioclase feldspar and pyroxene.
- Hardness
- 6-7 Mohs
- Color
- dark grey to black (weathered to brown)
- Luster
- dull/earthy
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black (weathered to brown); Luster: dull/earthy; Texture: fine-grained (aphanitic); Composition: 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. This specimen shows typical weathering from being in a fluvial or soil environment.
Uses & applications
Basalt is used heavily in the construction industry as aggregate for concrete, road base, and railroad ballast. Dense varieties are used for floor tiles and architectural accents.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also common on the Moon (forming the dark 'maria' or seas) and on Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (high density), and lack of visible crystals to the naked eye. It often breaks along irregular surfaces unless it displays columnar jointing.
