metamorphic
River Rock (likely Quartzite or Chert)
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Mottled gray, tan, and brown; Luster: Waxy to dull (smooth due to water erosion); Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- Mottled gray, tan, and brown
- Luster
- Waxy to dull (smooth due to water erosion)
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Physical properties
Hardness: 7 (Mohs scale); Color: Mottled gray, tan, and brown; Luster: Waxy to dull (smooth due to water erosion); Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. This specific specimen has been further shaped and polished by the mechanical weathering of a river or stream environment.
Uses & applications
Commonly used in landscaping, decorative ground cover, and as an aggregate in construction. High-purity quartzite is also used to produce silica sand for glass making.
Geological facts
River rocks are 'clastic' in a geological sense when found in riverbeds, but the individual rock itself here is a metamorphic specimen that has survived thousands of years of tumbling.
Field identification & locations
Identify in the field by its smooth, rounded 'potato' shape and extreme hardness—it will easily scratch glass. Usually found in current or ancient riverbeds and glacial deposits.
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