metamorphic
Quartzite (River Stone)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: yellowish-tan to grey; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- yellowish-tan to grey
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: yellowish-tan to grey; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.65.
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. This specimen shows significant river-worn rounding, indicating a history of fluvial transport over long geological periods.
Uses & applications
Used as decorative gravel, in landscaping, as a construction aggregate, and occasionally as a source of high-purity silica for electronic industrial processes.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, ending up as the rounded cobbles found in riverbeds like this specimen. It is harder than steel.
Field identification & locations
Identified by its extreme hardness (cannot be scratched by a steel nail), conchoidal or 'rounded' fracture edges, and grainy appearance under a lens. Common in glacial till and river beds worldwide.
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