sedimentary
Sedimentary rock with quartz veining
Laminated siltstone or mudstone with hydrothermal quartz veins
Hardness: 3-4 (matrix), 7 (veins); Color: Gray to blue-gray with white or tan banding; Luster: Dull to earthy; structure: fine-grained clastic with secondary mineralization.
- Hardness
- 3-4 (matrix), 7 (veins)
- Color
- Gray to blue-gray with white or tan banding
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (matrix), 7 (veins); Color: Gray to blue-gray with white or tan banding; Luster: Dull to earthy; structure: fine-grained clastic with secondary mineralization.
Formation & geological history
Formed from the lithification of fine-grained sediment (silt or clay) in a low-energy aquatic environment. The parallel bands (veins) formed later when mineral-rich fluids (likely silica) filled fractures in the rock, a process often associated with tectonic stress.
Uses & applications
Primarily of geological interest; common field rocks are sometimes used in landscaping, road fill, or as decorative garden stones.
Geological facts
This specimen is a classic example of 'cross-cutting relationships' in geology—the white veins are younger than the gray rock they penetrate. Such rocks are common in areas that have undergone historical mountain building.
Field identification & locations
Identify in the field by checking for harder, raised white lines crossing the softer darker rock. Often found in riverbeds, glacial till, or ancient lake deposits.
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