igneous
Basalt (with possible quartz veinsing)
Basalt
Hardness: 6 (Mohs scale); Color: Dark grey to black with white secondary mineral veins; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained/microscopic); Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black with white secondary mineral veins
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black with white secondary mineral veins; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained/microscopic); 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 very near the Earth's surface. This specimen appears to have undergone secondary mineralization where silica-rich fluids filled fractures to create the white veins.
Uses & applications
Commonly used as aggregate in construction (roads and concrete), railroad ballast, and ground-up for industrial abrasives. Polished basalt is also used for decorative flooring 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 other celestial bodies including the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible crystals. It is commonly found in volcanic regions, near ocean ridges, and as water-worn pebbles in riverbeds or beaches near volcanic outflows.
