igneous
Basalt with Quartz Veining
Veined Basalt (composed primarily of plagioclase feldspar, pyroxene, and olivine with quartz/calcite infill)
Hardness: 6 (basalt matrix) to 7 (quartz veins); Color: Dark grey to black matrix with white or translucent veins; Luster: Dull/earthy for matrix, vitreous for veins; Crystal structure: Aphanitic (fine-grained); Cleavage: None
- Hardness
- 6 (basalt matrix) to 7 (quartz veins)
- Color
- Dark grey to black matrix with white or translucent veins
- Luster
- Dull/earthy for matrix, vitreous for veins
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Physical properties
Hardness: 6 (basalt matrix) to 7 (quartz veins); Color: Dark grey to black matrix with white or translucent veins; Luster: Dull/earthy for matrix, vitreous for veins; Crystal structure: Aphanitic (fine-grained); Cleavage: None
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The white veins formed later when mineral-rich hydrothermal fluids filled fractures in the rock, typically during tectonic activity or burial metamorphism.
Uses & applications
Commonly used as crushed stone for construction, road base, and concrete aggregate. Attractive specimens are used as river stones for landscaping or polished as decorative pocket stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The white veins are 'scars' that show where the rock once cracked and healed under intense pressure and heat.
Field identification & locations
Identify by its heavy weight, dark color, and fine texture. The white veins will not scratch with a copper penny but will scratch glass if they are quartz. Commonly found in volcanic regions, riverbeds, and glacial deposits.
