igneous
Basalt
Mafic Igneous Rock (composed primarily of Pyroxene and Plagioclase Feldspar)
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, often weathering to green or brown; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to black, often weathering to green or brown
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to black, often weathering to green or brown; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. Basalt comprises most of the ocean floor and is found across all geological ages, notably in Large Igneous Provinces.
Uses & applications
Used extensively in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in the manufacturing of stone wool (insulation material) and occasionally as a high-durability floor tile.
Geological facts
Basalt is the most common rock on the Earth's surface and also covers large areas of the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt-jointing.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystals to the naked eye. Commonly found in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.
