metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, to tan; Luster: vitreous (glassy) to waxy; Structure: granular, non-foliated; Cleavage: none (fractures conchoidally)
- Hardness
- 7 on Mohs scale
- Color
- white, gray, to tan
- Luster
- vitreous (glassy) to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, to tan; Luster: vitreous (glassy) to waxy; Structure: granular, non-foliated; Cleavage: none (fractures conchoidally)
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, obliterating original textures.
Uses & applications
Used extensively in road construction, as railway ballast, for decorative building stone, countertops, and in some glassmaking processes.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges and hills over millions of years. It is often confused with marble, but quartzite is much harder and will not react with acid.
Field identification & locations
Identify by its extreme hardness (it will scratch glass) and its sugary, granular surface that breaks across individual grains rather than around them. Found globally in ancient mountain belts.
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