metamorphic
Quartzite
Crystalline silica (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish stains from iron oxides; Luster: vitreous to waxy; Structure: non-foliated, granular texture of interlocking quartz crystals; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or reddish stains from iron oxides; Luster: vitreous to waxy; Structure: non-foliated, granular texture of interlocking quartz crystals; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into an extremely hard rock network.
Uses & applications
Used in construction as crushed stone for road beds or railway ballast, as decorative building stone (veneers, flooring), and in glass manufacturing if the silica content is sufficiently high.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, forming the peaks of many mountain ranges. It is harder than steel and will scratch glass easily.
Field identification & locations
Identify in the field by its hardness (will scratch a knife blade) and the way it breaks: unlike sandstone which breaks around grains, quartzite breaks across the grains. Commonly found in folded mountain belts.
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