sedimentary
Quartz Cobble (with Iron Oxide Staining)
Microcrystalline to Macro crystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: White, cream, with yellow/brown iron staining; Luster: Vitreous to waxy when wet; Crystal Structure: Hexagonal (trigonal); Specific Gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- White, cream, with yellow/brown iron staining
- Luster
- Vitreous to waxy when wet
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Physical properties
Hardness: 7 (Mohs scale); Color: White, cream, with yellow/brown iron staining; Luster: Vitreous to waxy when wet; Crystal Structure: Hexagonal (trigonal); Specific Gravity: 2.65
Formation & geological history
Formed through hydrothermal processes or within igneous rocks like granite, subsequently weathered, transported by water (rivers/streams), and rounded over time into a cobble. Ages vary from millions to billions of years.
Uses & applications
Used as construction aggregate, in landscaping, and occasionally as lapidary material for tumbling or carving. High-purity quartz is used in glassmaking and electronics.
Geological facts
Quartz is the second most abundant mineral in Earth's continental crust. These rounded river stones are often referred to as 'river rats' or 'river rocks' and their smoothness is a direct result of mechanical erosion during transport.
Field identification & locations
Identified by its hardness (can scratch glass), lack of cleavage, and rounded shape. Commonly found in riverbeds, creek bottoms, and glacial deposits. Collectors value them for lapidary work or aquarium decor.
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