metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink/red/tan due to iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal/microcrystalline); Cleavage: none (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, but pink/red/tan due to iron oxides
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink/red/tan due to iron oxides; Luster: vitreous to dull; Crystal structure: hexagonal (internal/microcrystalline); Cleavage: none (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. Most deposits range from Proterozoic to Paleozoic eras.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. Historically used for making stone tools. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering to form the peaks of mountain ranges. It is significantly harder and more durable than the sandstone from which it originated.
Field identification & locations
Identify in the field by its ability to scratch glass and its granular, sugary appearance on fresh surfaces. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. Found globally in fold mountain belts.
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