metamorphic
River Stone (Quartzite/Chert)
Metamorphosed Quartz-rich Sedimentary Rock
Hardness: 7 (Mohs scale); Color: Muted brown, tan, and reddish-grey; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture when broken); Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Muted brown, tan, and reddish-grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Muted brown, tan, and reddish-grey; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture when broken); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone (quartzite) or the sedimentation of microcrystalline silica (chert). This specific specimen shows high degrees of water-rounding, likely originating from a riverbed or ancient alluvial deposit.
Uses & applications
Commonly used in landscaping, as aggregate in construction, or as decorative filler for pathways. Polished versions are often used in ornamental crafts and aquariums.
Geological facts
River stones like this are polished naturally by the abrasive action of water and other sediments over thousands of years. The reddish tint is often caused by iron oxide (hematite) staining.
Field identification & locations
Identify in the field by its smooth, rounded egg-like shape and extreme hardness (it will easily scratch glass). Found globally in riverbeds, glacial tills, and coastal beaches.
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