metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish due to iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Cleavage: none; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pinkish due to iron oxide
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish due to iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Often found in orogenic belts (mountain-building areas).
Uses & applications
Used in construction as crushed stone, road ballast, and decorative stone. Historically used for stone tools. Higher purity versions are used to make glass and silicon ceramics.
Geological facts
Quartzite is so tough that it often breaks through the constituent sand grains rather than around them, which distinguishes it from sandstone. Many mountain peaks are capped with quartzite because it is highly resistant to weathering.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and its sugary/crystalline texture. It is commonly found in riverbeds as rounded cobbles like this specimen, or in craggy mountain outcrops.
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