metamorphic
Quartzite
Metamorphic Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: Typically pink, red, white, gray, or yellowish due to iron oxide impurities. Luster: Vitreous to greasy on broken surfaces, sugary texture. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None (fractures conchoidally through grains).…
- Hardness
- 7 on the Mohs scale
- Luster
- Vitreous to greasy on broken surfaces, sugary texture
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Physical properties
Hardness: 7 on the Mohs scale. Color: Typically pink, red, white, gray, or yellowish due to iron oxide impurities. Luster: Vitreous to greasy on broken surfaces, sugary texture. Crystal structure: Trigonal (microcrystalline quartz grains fused together). Cleavage: None (fractures conchoidally through grains). Specific gravity: 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone or chert. Under high heat and tectonic pressure, the original quartz grains recrystallize and fuse together with interlocking quartz crystals, making it extremely durable.
Uses & applications
Used widely in construction as crushed stone for roadbeds, railway ballast, building stone, and manufacturing of silica brick and ferrosilicon. Higher purity varieties are used in glassmaking.
Geological facts
Because quartzite is harder and much more resistant to weathering than most other rocks, it frequently forms prominent ridges, hills, and mountain peaks (such as Baraboo Quartzite in Wisconsin).
Field identification & locations
Can be identified in the field by its sugary, interlocking grain texture and the fact that it does not fizz with hydrochloric acid and cannot be scratched by a steel knife (Mohs hardness > 5.5). Found globally in mountainous and ancient cratonic regions.
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