metamorphic
Quartzite River Rock
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Off-white, grey, yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8.
- Hardness
- 7 (Mohs scale)
- Color
- Off-white, grey, yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Off-white, grey, yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.8.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure. The smooth, rounded shape is the result of mechanical weathering and erosion, likely in a river or fluvial environment over thousands of years.
Uses & applications
Used as decorative landscaping stones, raw material for glass manufacturing, high-quality construction aggregate, and occasionally for lapidary work (tumbling).
Geological facts
Quartzite is so hard that it will scratch glass and even steel. Unlike sandstone, quartzite breaks through the quartz grains rather than around them due to the intense fusion of crystals during metamorphism.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and its grainy, granular appearance that looks like sandpaper but feels smooth. Found in riverbeds and glacial deposits worldwide.
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