igneous
Basalt with Quartz Veins
Basalt (SiO2 range 45-52%)
Hardness: 6-7 (Mohs scale); Color: Dark grey to black with white/grey veins; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to black with white/grey veins
- Luster
- Dull to vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to black with white/grey veins; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of basaltic lava at or very near the Earth's surface. The white veins represent secondary mineralization where silica-rich fluids filled fractures in the cooling rock.
Uses & applications
Commonly used as aggregate in construction, road base, and decorative landscaping stones. Polished versions are sometimes used for massage stones or pocket stones.
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, heavy, fine-grained matrix and the presence of criss-crossing quartz or calcite veins. Commonly found on beaches or in glacial till where it has been rounded by erosion.
