igneous
Basalt (with possible alteration or lichen)
Mafic volcanic rock (primarily Plagioclase and Pyroxene)
Hardness: 5-6 (Mohs); Color: Dark grey to black with light grey weathered patches; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black with light grey weathered patches
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black with light grey weathered patches; Luster: Dull/Sub-metallic; Structure: Fine-grained/Aphanitic; 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 Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Commonly used in construction as aggregate, in road building, as railroad ballast, and sometimes in stone carving or as high-strength insulation (mineral wool).
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 found on the Moon and Mars.
Field identification & locations
Identify by its dark color, high density, and fine-grained texture. It often breaks with a conchoidal or irregular fracture. Found in volcanic plateaus or near ocean ridges.
