metamorphic
Quartzite
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, but pink or reddish due to iron oxide staining; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal 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, but pink or reddish due to iron oxide staining; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together, creating a hard, dense rock. Occurs in mountain-building regions.
Uses & applications
Used as a decorative stone in architecture, a source of silica for glassmaking, railway ballast, and in construction as road aggregate. Often used for counter tops and floor tiles due to its hardness.
Geological facts
Quartzite is so hard that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone. It is often more weather-resistant than the surrounding rocks, frequently forming the tops of ridges and hills.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will easily scratch glass and steel). Commonly found in Precambrian or Paleozoic shield areas and mountain ranges like the Appalachians or Alps. Collectors look for unique color banding or crystalline inclusions.
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