metamorphic
Quartzite (Milky or Cloudy Quartz variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: White, tan, or grayish with translucent patches; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- White, tan, or grayish with translucent patches
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, tan, or grayish with translucent patches; Luster: Vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: Indistinct/Conchoidal fracture; Specific gravity: 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize into a dense, interlocking mosaic of quartz crystals. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Used as crushed stone for road construction and railway ballast; in industrial glass manufacturing; and as a decorative stone in landscaping or carving.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, frequently capping hills and mountain ridges. It is often confused with marble, but can be distinguished because it will scratch glass and does not fizz in acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and its grainy, sugary appearance on fresh surfaces. Common in mountain ranges and as rounded river pebbles.
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