metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: tan, white, or light pink due to iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale
- Color
- tan, white, or light pink due to iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, white, or light pink due to iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under intense heat and pressure, quartz grains in sandstone recrystallize and fuse together into a dense, hard rock. This process can occur over various geological ages, often in mountain-building zones.
Uses & applications
Used as a decorative stone in landscaping, a aggregate in road construction, and for manufacturing glass or silica-based industrial products. In prehistoric times, it was used for making stone tools.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, leading to the formation of prominent ridges and peaks in mountain ranges.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sugary, granular appearance. Unlike sandstone, when quartzite breaks, it breaks through the quartz grains rather than around them. It is very common in folded mountain belts globally.
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