sedimentary
Quartz-Veined Mudstone
Argillite or Mudstone with Quartz Veining (SiO2 in Siliciclastic Matrix)
Hardness: 3-4 (matrix) / 7 (veins); Color: Reddish-brown matrix with white/cream veins; Luster: Dull to earthy; Structure: Fine-grained clastic; Cleavage: None (conchoidal fracture on veins)
- Hardness
- 3-4 (matrix) / 7 (veins)
- Color
- Reddish-brown matrix with white/cream veins
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (matrix) / 7 (veins); Color: Reddish-brown matrix with white/cream veins; Luster: Dull to earthy; Structure: Fine-grained clastic; Cleavage: None (conchoidal fracture on veins)
Formation & geological history
Formed from the lithification of silt and clay. The characteristic white lines (veins) were created when tectonic stress caused the rock to fracture, allowing silica-rich hydrothermal fluids to circulate through the cracks and crystallize into quartz.
Uses & applications
Commonly used as decorative garden stones, in landscaping, or as tumbling rough for amateur geologists. Occasionally used as low-grade construction fill.
Geological facts
The 'spiderweb' pattern of veins is a record of ancient seismic or tectonic activity. These specimens are often water-worn, smoothed by the action of rivers or beaches.
Field identification & locations
Identify in the field by looking for fine-grained dark rocks intersected by hard, light-colored mineral lines that cannot be scratched by a steel knife. Frequently found in riverbeds and coastal regions.
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