metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, white, grey (can be reddish/brown due to iron); Luster: Vitreous to dull; Structure: Granular, non-foliated crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, white, grey (can be reddish/brown due to iron)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, white, grey (can be reddish/brown due to iron); Luster: Vitreous to dull; Structure: Granular, non-foliated crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed from quartz-rich sandstone subjected to extreme heat and pressure (regional or contact metamorphism). The sand grains recrystallize into a dense interlocking network of quartz crystals.
Uses & applications
Used as crushed stone for road construction, railroad ballast, decorative landscaping, flooring, and historically for stone tools due to its fracture patterns.
Geological facts
Quartzite is so hard that it will scratch glass. It is much more durable than its parent rock, sandstone, and is highly resistant to chemical weathering, often forming the caps of ridges and mountains.
Field identification & locations
Identify by its hardness (scratches steel and glass) and granular 'sugary' appearance. Unlike sandstone, when broken, quartzite fractures through the grains rather than around them. Common in old mountain belts globally.
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