metamorphic
River Cobble (likely Quartzite or Chert)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Brown, tan, and reddish-orange; Luster: Dull to waxy; Structure: Microcrystalline; Specific Gravity: Approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Brown, tan, and reddish-orange
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, tan, and reddish-orange; Luster: Dull to waxy; Structure: Microcrystalline; Specific Gravity: Approx 2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone or the deposition of silica-rich sediments. The rounded shape indicates extensive transport and erosion by water in a high-energy river or beach environment.
Uses & applications
Used primarily as decorative landscaping stone, drainage aggregate, and in construction; can be polished for lapidary art.
Geological facts
River cobbles like this one often travel hundreds of miles from their source, becoming smoother and rounder as they knock against other stones in moving water. Traces of iron oxides give this specimen its reddish-brown tint.
Field identification & locations
Identify in the field by its smooth, water-worn surface and extreme hardness (will scratch glass). Commonly found in dry creek beds, river banks, and glacial deposits.
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