metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, tan, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white, tan, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, tan, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. This specific specimen has been further shaped and smoothed by water transport in a river or stream environment.
Uses & applications
Used as decorative landscaping stone, in construction as crushed aggregate, and occasionally as a source of silica for glass making. High-quality pieces are used for architectural facings.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming resistant ridges. It is harder than steel, meaning it will easily scratch a knife blade.
Field identification & locations
Identify by its hardness (cannot be scratched by steel) and the way it breaks through the grains rather than around them. Commonly found in riverbeds, glacial tills, and mountainous regions worldwide.
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