metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale (scratches glass); Color: White, gray, or pale pink; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular texture; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- White, gray, or pale pink
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass); Color: White, gray, or pale pink; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular texture; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz sand grains to recrystallize and fuse together. It can range in age from Precambrian to much more recent periods.
Uses & applications
Used extensively in construction as crushed stone for road base, railway ballast, and roofing granules. Polished slabs are used for countertops, flooring, and decorative wall cladding due to its durability and resistance to chemicals.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks; when broken, the fracture travels through the quartz grains rather than along their boundaries, unlike parent sandstone. It is frequently mistaken for marble but is much harder and won't react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch a steel knife or glass) and its grainy, sugary appearance. It is commonly found in mountain folds (appalachians, Alps) and cratonic areas like the Lake Superior region.
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