metamorphic
Quartzite
Quartzite (SiO2-dominant rock)
Hardness: 7 on Mohs scale; Color: typically white to gray, often yellow, pink, or red due to iron impurities; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none, breaks with a conchoidal or irregular splintery 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 yellow, pink, or red due to iron impurities; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none, breaks with a conchoidal or irregular splintery 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 together into a dense, hard rock. Found in mountain belts globally.
Uses & applications
Used in construction for road ballast, roofing granules, and as a decorative building stone. High-purity quartzite is used in glassmaking and to produce silicon metal. Hard enough for use as an abrasive.
Geological facts
Quartzite is so tough that it often survives deep weathering to form prominent ridges and mountain peaks. It is frequently mistaken for marble, but unlike marble, it will not fizz when exposed to acid and is hard enough to scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will easily scratch a steel knife blade). Commonly found in Precambrian shield areas and orogenic belts. Collectors look for pieces with interesting color banding or distinct recrystallization.
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