metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (hexagonal); Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). Most quartzite is Proterozoic to Paleozoic in age.
Uses & applications
Used in construction as crushed stone for road gravel, as a decorative stone in architecture (countertops, tiles), and as a source of high-purity silica for glassmaking and industrial abrasives.
Geological facts
Quartzite is so durable that it often forms the resistant ridges and hilltops of mountain ranges. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and its granular, sugary texture. It is commonly found in metamorphic terranes worldwide, such as the Appalachian Mountains or the Alps.
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