igneous
Quartz Veined Basalt Pebble
Amygdaloidal Basalt with Quartz (SiO2) veining
Hardness: 6-7 (Mohs); Color: Dark gray to black matrix with white or translucent veins; Luster: Dull matrix with vitreous/glassy veins; Structure: Microcrystalline with hydrothermal fracture-filling; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 (Mohs)
- Color
- Dark gray to black matrix with white or translucent veins
- Luster
- Dull matrix with vitreous/glassy veins
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark gray to black matrix with white or translucent veins; Luster: Dull matrix with vitreous/glassy veins; Structure: Microcrystalline with hydrothermal fracture-filling; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of basaltic lava. The white veins represent a later secondary geological event where hydrothermal fluids (hot water rich in silica) filled cracks in the rock and crystallized into quartz over millions of years.
Uses & applications
Primarily used as decorative landscaping stone or beach/river gravel. High-quality smooth pebbles are used in massage therapy and aquarium decor. Basalt is also used in construction as crushed aggregate.
Geological facts
These rocks are often called 'Wishing Stones' by beachcombers if a single white line circles the entire stone without breaking. The white quartz is much harder than the basalt matrix, often causing the vein to stand out in relief as the rock weathers.
Field identification & locations
Identify in the field by the distinct high-contrast white stripes against a dark, dense, fine-grained background. Can be found in volcanic regions or along coastlines and riverbeds where water has naturally tumbled the rock smooth.
