metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, or white with a sugary texture; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, or white with a sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, or white with a sugary texture; 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 regional metamorphism of quartz-rich sandstone, where the sandstone is subjected to intense heat and pressure, causing the sand grains to recrystallize and fuse together.
Uses & applications
Used in construction as a decorative stone, railway ballast, road aggregate, and as a source of silica in industrial processes or manufacturing glass.
Geological facts
Quartzite is so strong that when it breaks, the fracture passes through the quartz grains themselves rather than around them, unlike the sandstone from which it originated. It is resistant to chemical weathering.
Field identification & locations
Identify in the field by its hardness (it will scratch glass/steel) and grainy 'sugary' appearance on fresh surfaces. Often found in mountainous regions or as rounded river cobbles due to its durability.
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