sedimentary
Greywacke with Quartz Vein
Matrix: Impure Sandstone (SiO2 + varied clasts), Veins: Quartz (SiO2)
Hardness: 6-7 (quartz/matrix), Color: Dark grey with white veins, Luster: Vitreous to dull, Crystal Structure: Trigonal (quartz), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 6-7 (quartz/matrix), Color: Dark grey with white veins, Luster: Vitreous to dull, Crystal Structure: Trigonal (quartz), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through rapid deposition in deep marine environments (turbidity currents). The white veins formed later when hydrothermal fluids filled tectonic fractures and crystallized. Primarily Paleozoic to Mesozoic in age.
Uses & applications
Commonly used in construction as road base, railroad ballast, and concrete aggregate. Usually has low jewelry value but interest for educational displays.
Geological facts
The white lines are called 'veins' and represent 'fossilized' movement of water through the rock under high pressure deep in the Earth's crust.
Field identification & locations
Identify by a dark, hard, fine-grained matrix that cannot be scratched by a knife, cross-cut by harder white lines. Found frequently in coastal regions and mountain belts (orogenic zones) like the Alps or Appalachians.
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