metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or brown (tan); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or brown (tan)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or brown (tan); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. Typically found in orogenic (mountain-building) belts.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a raw material for glass and ceramics due to high silica content. Small pieces serve as landscape gravel.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them, which distinguishes it from sandstone. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (scratches glass) and grainy, sugary texture. Common in ancient mountain ranges and glacial till. Collectors look for pieces with interesting mineral inclusions or distinct colors.
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