metamorphic
Quartzite (Quartz-rich Cobble)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light tan/pink; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- White to light tan/pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light tan/pink; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the quartz grains, locking them into a very hard matrix. This specimen appears weathered and rounded by fluvial (water) action.
Uses & applications
Used primarily in construction for road ballast, railroad tracks, and concrete aggregate. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges or hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and sugary, crystalline texture on a fresh break. It often has a 'sparkling' appearance in sunlight due to recrystallized planes.
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