metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: tan, gray, or white with iron staining; Luster: vitreous to dull; Structure: non-foliated, granular; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- tan, gray, or white with iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, gray, or white with iron staining; Luster: vitreous to dull; Structure: non-foliated, granular; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Often found in orogenic belts and tectonic plate boundaries.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and high-quality building stone. Also used as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along the boundaries between them, unlike sandstone which breaks around the grains.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture. Commonly found in riverbeds as rounded cobbles like this specimen.
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