metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to tan/buff; Luster: Vitreous to dull; Crystal structure: Non-foliated interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to tan/buff
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to tan/buff; Luster: Vitreous to dull; Crystal structure: Non-foliated interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the sand grains to recrystallize and fuse together. Often found in Precambrian or Paleozoic mountain belts.
Uses & applications
Used as crushed stone in road construction and railroad ballast, for glass making due to high silica content, and as decorative stone in landscaping or architectural cladding.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming resistant ridges and hilltops. It will scratch glass easily, unlike similar-looking limestone.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel nail) and grainy, sugar-like texture where the individual grains have fused. Commonly found in riverbeds or near mountain ranges.
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