Igneous
Crushed Rock (Basalt)
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) due to rapid cooling; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to charcoal black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic) due to rapid cooling; Cleavage: None; 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. These are volcanic in nature and can date from recent eruptions to billions of years old.
Uses & applications
Extensively used in construction as aggregate for concrete and asphalt, road base, and railroad ballast. Some varieties are used in architectural stone and landscaping.
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 (density), and lack of visible large crystals to the naked eye. Commonly found in quarries and near volcanic regions. Not rare for collectors, but essential for geological studies.
