metamorphic
River Rock (Quartzite/Chert conglomerate)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or light grey; Luster: Waxy to dull (river tumbled); Crystal Structure: Cryptocrystalline or interlocking micro-crystals; Cleavage: None; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or light grey
- Luster
- Waxy to dull (river tumbled)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or light grey; Luster: Waxy to dull (river tumbled); Crystal Structure: Cryptocrystalline or interlocking micro-crystals; Cleavage: None; Specific Gravity: 2.6-2.7.
Formation & geological history
Originally formed from quartz-rich sandstone that underwent intense heat and pressure (metamorphism). This specific specimen has been further shaped and smoothed by fluvial (river) erosion over many years.
Uses & applications
Used in landscaping, decorative ground cover, aquarium decor, and sometimes as a base material in construction. Rounded rocks like this are often used in 'river stone' massage therapy.
Geological facts
Quartzite is one of the most durable rocks on the Earth's surface. Because of its hardness, it often survives long-distance transport in rivers that would break down softer rocks like shale or limestone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, water-worn exterior. Commonly found in riverbeds, glacial deposits, and coastal beaches.
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