metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 (Mohs scale); Color: White, grey, or tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific gravity: approx. 2.6
- Hardness
- 7 (Mohs scale)
- Color
- White, grey, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grey, or tan; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific gravity: approx. 2.6
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the individual quartz grains to recrystallize and fuse together. Typically associated with regional metamorphism in mountain-building zones.
Uses & applications
Used primarily in construction as crushed stone for roadbeds, railroad ballast, and building stone. High-purity quartzite is used in glassmaking and electronics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or rugged peaks of mountain ranges because it resists weathering better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that doesn't rub off. Found globally in ancient tectonic plates.
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