metamorphic
Quartzite
Quartzite (principally Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize and fuse together. It is found in mountain belts and shield areas worldwide.
Uses & applications
Used as a decorative stone in landscaping, as an abrasive, in construction as crushed stone for road ballast, and in the production of glass and ceramics. High-purity quartzite is a source of silica.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it weathers more slowly than the surrounding rock. It is often confused with marble but can be distinguished by its hardness (it scratches glass).
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (cannot be scratched by a steel knife). Common in riverbeds and mountainous glacial deposits as rounded cobbles.
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