metamorphic
Quartzite
Quartzite (Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or pink
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or pink; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; 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 into a dense rock.
Uses & applications
Used extensively in road construction, as railway ballast, for flooring and wall tiles, and occasionally in jewelry as a substitute for more expensive stones.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and mountains. It is harder than a steel knife and will scratch glass.
Field identification & locations
Identify by its hardness (scratches glass) and its grainy, sugary appearance where it has been freshly broken. Common in mountain ranges and ancient metamorphic shields.
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