igneous
Basalt
Mafic Igneous Rock (composed primarily of Pyroxene and Plagioclase Feldspar)
Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic (if metallic minerals present); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic (if metallic minerals present)
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic (if metallic minerals present); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.9-3.1
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 rock type in the Earth's crust, forming most of the ocean floor.
Uses & applications
Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. Also used as dimension stone for tiles and monuments.
Geological facts
Basalt is the most voluminous rock on the Earth's surface and also covers large areas of the Moon (the dark lunar maria), Mars, and Venus. It is the source of rich volcanic soils.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. In the field, it often forms cooling columns (hexagonal) if in large flows.
