metamorphic
Quartzite (or Milky Quartz)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale. Color: Off-white, yellowish-tan to pinkish light brown due to iron oxide staining. Luster: Vitreous to greasy. Crystal System: Hexagonal (trigonal). Cleavage: None (conchoidal to uneven fracture). Specific Gravity: ~2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on Mohs scale. Color: Off-white, yellowish-tan to pinkish light brown due to iron oxide staining. Luster: Vitreous to greasy. Crystal System: Hexagonal (trigonal). Cleavage: None (conchoidal to uneven fracture). Specific Gravity: ~2.65.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing quartz grains to recrystallize and interlock tightly. Can also form as massive vein quartz precipitated from hydrothermal fluids.
Uses & applications
Used as crushed stone in construction, road aggregates, and ballast. High-purity quartzite is used in glassmaking and metallurgy. Rough specimens are commonly collected by rockhounds.
Geological facts
Quartzite is extremely tough and resistant to chemical and physical weathering. Unlike sandstone which breaks along sand grains, quartzite breaks across or through the quartz grains.
Field identification & locations
Identify in the field by its high hardness (scratches glass easily, cannot be scratched by steel) and tightly interlocking glassy texture with conchoidal fractures. Extremely common worldwide in metamorphic terrains and mountain belts.
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