metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with reddish-brown staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white with reddish-brown staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with reddish-brown staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in convergent plate boundaries. This causes the quartz grains to recrystallize and fuse into a dense rock.
Uses & applications
Used primarily as crushed stone for road construction and railway ballast. Due to its resistance to weathering and hardness, it is also used for building facades and countertops.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along the boundaries between them, unlike sandstone. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its tendency to have a sugary appearance on fresh surfaces. It is found in mountain ranges worldwide, such as the Appalachians and the Alps.
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