metamorphic
Red Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Pink to reddish-brown due to hematite impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Pink to reddish-brown due to hematite impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Pink to reddish-brown due to hematite impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (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 quartz grains to recrystallize and fuse together. Red varieties often date back to the Proterozoic eon.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. Durable for landscaping and occasionally used as a decorative stone in jewelry (cabochons).
Geological facts
Quartzite is so hard and chemically resistant that it often forms the crests of ridges because it resists erosion better than the surrounding rock. It can scratch glass and steel easily.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (it will not be scratched by a knife). Commonly found in mountainous regions or ancient cratons like the Siouan Quartzite in the Midwestern USA.
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