metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to yellowish-gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to yellowish-gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to yellowish-gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. The original quartz grains recrystallize into a dense, interlocking mosaic.
Uses & applications
Used as a decorative stone in construction, road ballast, railway tracks, and sometimes as a source of silica for glass manufacturing and metallurgy.
Geological facts
Quartzite is so tough that it often outlasts surrounding rocks, forming distinctive ridges or mountainous peaks in the landscape. It is sometimes mistaken for white marble, but it does not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass easily) and its sugary, granular appearance. Commonly found in folded mountain belts globally. To distinguish it from sandstone, observe that fractures will cut through the grains rather than around them.
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