igneous
Basalt
Basalt (Aphanitic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brownish-red; Luster: Dull/Sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black, often weathering to brownish-red
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black, often weathering to brownish-red; Luster: Dull/Sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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. Most common rock in Earth's crust, primarily forming the ocean floor.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and high-temperature insulation (stone wool). Also used for floor tiles and statues.
Geological facts
Basalt is the most common volcanic rock on Earth. It also makes up most of the surface of the Moon, Mars, and Venus, appearing as dark regions known as 'maria'.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. It often shows vesicular (pitted) texture or columnar jointing in large outcrops. Common in volcanic regions.
