metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink (this specimen shows iron oxidation); Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific gravity: 2.63 - 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink (this specimen shows iron oxidation); Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture; Specific gravity: 2.63 - 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together. Specimens can vary in age from Proterozoic to more recent tectonic events.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-quality slabs are used for countertops, flooring, and decorative stone. Sometimes used in glass manufacturing if silica content is exceptionally high.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the peaks of ridges and mountains. It is harder and more durable than the sandstone from which it originated.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and the fact that it breaks across the sand grains rather than around them. Common in fold mountain belts and ancient shield areas.
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