metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, often with tan or yellowish staining from iron; Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal or uneven fracture; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to grey, often with tan or yellowish staining from iron; Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal or uneven fracture; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in orogenic belts. This causes the quartz grains to recrystallize and fuse together.
Uses & applications
Used as a decorative stone in construction, road ballast, railway tracks, and industrial glass-making due to high silica content.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass easily) and its sugary, granular texture. It is commonly found in mountain ranges and ancient shields worldwide.
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