igneous
Basalt with Quartz Veins
Aphanitic Mafic Igneous Rock (Main body: SiO2, Fe, Mg rich)
Hardness: 6 (basalt) / 7 (quartz); Color: Dark grey to charcoal with white veins; Luster: Dull/earthy matrix with vitreous veins; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 6 (basalt) / 7 (quartz)
- Color
- Dark grey to charcoal with white veins
- Luster
- Dull/earthy matrix with vitreous veins
Identified More igneous →
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Physical properties
Hardness: 6 (basalt) / 7 (quartz); Color: Dark grey to charcoal with white veins; Luster: Dull/earthy matrix with vitreous veins; Structure: Fine-grained/aphanitic; Specific Gravity: 2.8-3.0
Formation & geological history
The dark host rock formed from the rapid cooling of basaltic lava. The white veins formed later when tectonic activity fractured the rock, allowing silica-rich hydrothermal fluids to precipitate quartz into the cracks.
Uses & applications
Commonly used in landscaping, as river stones, in road construction (crushed), and as decorative aquarium stones.
Geological facts
The white lines are often called 'stress fractures' or 'healed cracks.' Finding a rock with a single continuous white band all the way around is sometimes called a 'Wishing Stone' in folklore.
Field identification & locations
Identified by the contrast between a dark, fine-grained matrix and hard, crystalline white veins. Common on beaches and in riverbeds where water erosion has rounded the pebble.
