igneous
Basalt with Calcite Veining
Aphanitic Mafic Igneous Rock (Basalt) with CaCO3
Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white streaks; Luster: Dull/earthy; Structure: Massive to fine-grained; Cleavage: None for basalt; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 (basalt) / 3 (calcite veins)
- Color
- Dark grey to black with white streaks
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white streaks; Luster: Dull/earthy; Structure: Massive to fine-grained; Cleavage: None for basalt; 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. The white veins formed later as mineral-rich groundwater deposited calcite into fractures.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Small specimens are used for teaching geological processes.
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
Identified by its dark color, fine-grained texture, and high density. The white veins will react (fizz) if a drop of weak acid is applied. Found in volcanic regions worldwide.
