metamorphic
Quartzite
Metamorphic Quartz Rock (SiO2)
Hardness: 7 on Mohs scale; Color: light gray to pale blue-gray; Luster: vitreous to sugary/grained; Crystal Structure: Trigonal (microcrystalline interlocked quartz grains); Cleavage: None (conchoidal to uneven fracture)
- Hardness
- 7 on Mohs scale
- Color
- light gray to pale blue-gray
- Luster
- vitreous to sugary/grained
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Physical properties
Hardness: 7 on Mohs scale; Color: light gray to pale blue-gray; Luster: vitreous to sugary/grained; Crystal Structure: Trigonal (microcrystalline interlocked quartz grains); Cleavage: None (conchoidal to uneven fracture)
Formation & geological history
Formed through regional or contact metamorphism of quartz-rich sandstone under high heat and pressure, causing quartz grains to recrystallize into a dense, interlocking mosaic.
Uses & applications
Used in construction as crushed stone, railway ballast, decorative building stone, countertop surfaces, and occasionally in glass manufacturing.
Geological facts
Quartzite is so tough and resistant to weathering that it often forms prominent ridges and hilltops. Unlike sandstone, which breaks around quartz grains, quartzite breaks right through the individual mineral grains.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass easily and cannot be scratched by a steel blade) and sugary texture on freshly broken surfaces. Commonly found in mountainous metamorphic terrains worldwide.
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