sedimentary
Graywacke with Quartz Veins
Argillaceous Sandstone (SiO2 composition in veins)
Hardness: 6-7 (quartz veins) 5-6 (matrix). Color: Dark gray/blue-gray with white horizontal bands. Luster: Dull/earthy matrix, vitreous veins. Structure: Clastic matrix with secondary hydrothermal filling.
- Hardness
- 6-7 (quartz veins) 5-6 (matrix)
- Color
- Dark gray/blue-gray with white horizontal bands
- Luster
- Dull/earthy matrix, vitreous veins
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Physical properties
Hardness: 6-7 (quartz veins) 5-6 (matrix). Color: Dark gray/blue-gray with white horizontal bands. Luster: Dull/earthy matrix, vitreous veins. Structure: Clastic matrix with secondary hydrothermal filling.
Formation & geological history
Formed in deep-water marine environments (turbidity currents) where sand and mud accumulate rapidly. The white bands are quartz veins formed later by silica-rich hydrothermal fluids filling cracks during tectonic movement.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and riprap. Also collected as decorative river stones or 'wishing stones'.
Geological facts
The white lines are often called 'wishing lines' in folklore. Geologically, these rocks provide evidence of high-energy underwater landslides and subsequent tectonic stress that fractured the rock.
Field identification & locations
Identified by its fine-grained, dark, hard matrix and distinct, protruding white crystalline lines. Commonly found on beaches and in riverbeds in orogenic (mountain-forming) belts.
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