metamorphic
Quartzite (with Milky Quartz)
SiO2 (Silicon Dioxide)
Hardness: 7 on Mohs scale; Color: grayish-white, milky white, tan/beige accents; Luster: vitreous to greasy; Crystal Structure: Trigonal (microcrystalline/interlocking aggregate); Cleavage: None (conchoidal to uneven fracture)
- Hardness
- 7 on Mohs scale
- Color
- grayish-white, milky white, tan/beige accents
- Luster
- vitreous to greasy
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: grayish-white, milky white, tan/beige accents; Luster: vitreous to greasy; Crystal Structure: Trigonal (microcrystalline/interlocking aggregate); Cleavage: None (conchoidal to uneven fracture)
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under high heat and pressure, causing quartz grains to recrystallize into a dense, interlocking matrix. Often smoothed by water transport (river or beach pebble).
Uses & applications
Commonly used in construction aggregate, landscaping, decorative stone, and aquascaping. High-purity quartzite is used to extract silicon for semiconductors and glassmaking.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering. When struck, quartzite breaks across its quartz grains, unlike sandstone which breaks around individual grains.
Field identification & locations
Identified by its high hardness (scratches glass), sugary-to-glassy textured surface, and rounded water-worn shape. Found in gravel beds, rivers, beaches, and glaciated regions globally.
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