metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None (conchoidal fracture through grains); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan with a sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None (conchoidal fracture through grains); 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 grains to recrystallize and fuse together into a dense, interlocking mosaic.
Uses & applications
Used extensively in construction as crushed stone for road gravel and railway ballast, as a dimension stone for flooring and wall coverings, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that unlike sandstone, which breaks around its individual sand grains, quartzite breaks directly through the grains. It is often resistant to weathering and frequently forms the crests of mountain ranges.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its crystalline, 'sugary' appearance when freshly broken. Found globally in folded mountain belts like the Appalachians or the Alps. For collectors, look for interlocking grains that lack the 'grittiness' of sandstone.
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