sedimentary
Siltstone with Quartz Vein
Siltstone (primarily SiO2, Al2O3, Fe2O3)
Hardness: 6-7 on Mohs scale; Color: Gray-green to dark gray with a thin white/yellowish quartz vein; Luster: Dull (matrix) to vitreous (vein); Structure: Fine-grained, clastic; Cleavage: None (conchoidal fracture likely).
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull (matrix) to vitreous (vein)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Gray-green to dark gray with a thin white/yellowish quartz vein; Luster: Dull (matrix) to vitreous (vein); Structure: Fine-grained, clastic; Cleavage: None (conchoidal fracture likely).
Formation & geological history
Formed from the lithification of silt-sized particles deposited in low-energy environments like river floodplains or lagoons. The vein formed later through hydrothermal activity where mineral-rich water filled rock fractures.
Uses & applications
Used primarily as low-grade construction aggregate or fill material. Smaller, uniquely patterned pieces are often kept as part of amateur rock collections or used as decorative garden stones.
Geological facts
Siltstone is the middle ground between sandstone and shale. The quartz vein seen here acts as a 'geological record' of the stress and fluid movement that occurred deep underground millions of years after the rock first formed.
Field identification & locations
Identify by its gritty texture (finer than sandstone, coarser than shale) and non-split layers. Common in sedimentary basins worldwide. In the field, look for thin, protruding bands of harder material (quartz) cutting across the softer matrix.
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