igneous
Basalt with Quartz Veins
Basalt (complex silicate) with Quartz (SiO2) intrusions
Hardness: 6-7 (Mohs); Color: Dark green to black with white banding; Luster: Dull to vitreous (waxy when wet); Structure: Fine-grained aphanitic with hydrothermal vein filling; Specific Gravity: 2.8–3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Dark green to black with white banding
- Luster
- Dull to vitreous (waxy when wet)
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark green to black with white banding; Luster: Dull to vitreous (waxy when wet); Structure: Fine-grained aphanitic with hydrothermal vein filling; 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 represent hydrothermal activity where mineral-rich water filled fractures in the basalt and crystallized over geological time, typically during the Cenozoic or Mesozoic eras.
Uses & applications
Common basalt is used in construction as aggregate or road base. Rounded river/beach specimens like this are used in landscape design, aquarium decor, and as 'worry stones' or decorative pebbles for collectors.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. When basalt contains white quartz or calcite veins, it creates a high-contrast look often called 'Zebra Stone' or 'Spider-web rock' depending on the vein pattern.
Field identification & locations
Identify in the field by its high density/weight, dark matrix, and the fact that the white veins will scratch glass (if quartz). Commonly found in volcanic regions, riverbeds, and coastal beaches. This specimen shows significant water-tumbled erosion, indicating it was found in a high-energy aquatic environment.
