igneous
Basalt Fragment
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull; Crystal Structure: Very fine-grained (aphanitic) due to rapid cooling; Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull; Crystal Structure: Very fine-grained (aphanitic) due to rapid cooling; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used in construction as road base, railroad ballast, and aggregate in concrete. Some dense varieties are used for high-end floor tiles or monuments.
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, heavy weight for its size, and lack of visible crystals. Commonly found in areas with historic volcanic activity or as decorative gravel.
