igneous
Basalt with Hematite staining
Extrusive mafic igneous rock with Fe2O3
Hardness: 5-6 (Mohs); Color: dark grey to black with reddish-brown edges; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- dark grey to black with reddish-brown edges
- Luster
- dull to earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: dark grey to black with reddish-brown edges; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The reddish staining indicates subsequent oxidation of iron minerals (hematite).
Uses & applications
Used primarily in construction as aggregate for roads, railroad ballast, and concrete. As a hand specimen, it is common for educational and amateur mineral collecting.
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 common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and very fine grains. Look for it in volcanic regions or in landscaping gravel (river rock).
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