metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to grainy; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with conchoidal fracture.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used in construction as crushed stone or decorative building stone, in glass manufacturing if pure enough, and as a natural abrasive.
Geological facts
Quartzite is so hard and chemically resistant that it often forms prominent ridges and hills while surrounding softer rocks erode away. It is tougher than the sandstone it originated from.
Field identification & locations
Identify by its extreme hardness (it will scratch glass) and lack of reaction to acid. It often appears sugary or sparkly when broken. Commonly found in mountain ranges and river gravels.
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