metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Vitreous to waxy (especially when wet); Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or gray
- Luster
- Vitreous to waxy (especially when wet)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Vitreous to waxy (especially when wet); Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the regional 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 as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping or as a smooth river rock/tumbled stone.
Geological facts
Quartzite is so hard that it can scratch steel and glass easily. Unlike sandstone which breaks around its grains, quartzite breaks right through the quartz grains because the matrix is as strong as the grains themselves.
Field identification & locations
Commonly found in riverbeds or coastal areas as water-worn pebbles. Look for a sugary texture and a hardness that cannot be scratched by a knife. These specimens are often rounded by long-term water erosion.
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