metamorphic
Quartzite (specifically Pink or Red Quartzite)
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale (scratches glass); Color: Pink to reddish-purple due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Granoblastic (interlocking crystals); Cleavage: None (breaks across grains/conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale (scratches glass)
- Color
- Pink to reddish-purple due to iron oxide impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (scratches glass); Color: Pink to reddish-purple due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Granoblastic (interlocking crystals); Cleavage: None (breaks across grains/conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together. These specimens often originate from Precambrian or Paleozoic formations.
Uses & applications
Used primarily in construction as crushed stone for road ballast, railway beds, and aggregate. High-quality slabs are used for countertops, flooring, and decorative lapidary work. It is also used as a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that unlike sandstone, which breaks around its individual grains, quartzite fractures through the grains. The pink color is often caused by tiny amounts of hematite (iron oxide) coating the original sand grains before metamorphism.
Field identification & locations
Identify in the field by its extreme hardness (it will not be scratched by a steel knife) and its grainy, sugary texture. It is commonly found in mountainous regions or glacial till. Notable locations include the Sioux Quartzite formation in the Midwestern USA and various Canadian Shield outcrops.
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