metamorphic
Quartzite (Iron-stained)
Metamorphosed Quartz-rich Rock (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan with yellow-orange iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan with yellow-orange iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan with yellow-orange iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together, creating an extremely durable rock. Primarily formed during mountain-building events in various geological eras.
Uses & applications
Used widely as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists weathering much better than surrounding rocks like shale or limestone.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks through the quartz grains rather than around them. Often found in mountainous regions near fault lines.
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