metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, yellow, or grey (due to iron oxides); Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, yellow, or grey (due to iron oxides)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, yellow, or grey (due to iron oxides); Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing recrystallization and interlocking of quartz grains. Most deposits date back to the Proterozoic or Paleozoic eras.
Uses & applications
Used as a decorative stone in landscaping, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. Unlike sandstone, quartzite will fracture through the grains rather than around them.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Commonly found in mountain belts and shield areas globally. Collectors look for sugary textures or rare color variations.
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