igneous
Basalt with Quartz Vein
Mafic Igneous Rock (Basalt) with SiO2 (Quartz) Vein
Hardness: 6-7 (Mohs). Color: Dark gray to black matrix with a distinct white horizontal band. Luster: Dull/Earthy for the basalt, Vitreous/Glassy for the quartz. Structure: Aphanitic (fine-grained) matrix.
- Hardness
- 6-7 (Mohs)
- Luster
- Dull/Earthy for the basalt, Vitreous/Glassy for the quartz
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Physical properties
Hardness: 6-7 (Mohs). Color: Dark gray to black matrix with a distinct white horizontal band. Luster: Dull/Earthy for the basalt, Vitreous/Glassy for the quartz. Structure: Aphanitic (fine-grained) matrix.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white quartz vein formed later when hydrothermal fluids rich in silica filled a crack in the cooling rock and crystallized.
Uses & applications
Common basalt is used in road base, railroad ballast, and concrete aggregate. Specimens with distinct veins are primarily collected for geological study or as landscape accents.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The presence of a clean, straight vein like this indicates a crack that opened under stress (brittle deformation) before mineral deposition.
Field identification & locations
Identify by its heavy weight (high specific gravity), dark color, and fine grain size. The vein will scratch glass while the dark rock might only barely do so. Commonly found in regions with historical volcanic activity.
