metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness of 7 on Mohs scale; color varies from white/gray to tan/brown due to iron staining; waxy to vitreous luster; granular texture; trigonal crystal system in individual grains; high specific gravity (~2.6-2.7).
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Physical properties
Hardness of 7 on Mohs scale; color varies from white/gray to tan/brown due to iron staining; waxy to vitreous luster; granular texture; trigonal crystal system in individual grains; high specific gravity (~2.6-2.7).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse into a solid, interlocking network. Most quartzite represents ancient beach or desert sands from millions of years ago.
Uses & applications
Used widely in construction as crushed stone for road ballast, roofing granules, and as a decorative stone in landscaping. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the peaks of mountains and ridges. It is often confused with marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks through quartz grains rather than around them. Commonly found in mountainous regions and riverbeds as rounded cobbles.
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