metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to intense heat and pressure (regional metamorphism), causing the individual quartz grains to recrystallize and fuse into a solid network of silica.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a raw material in the glass and silicate industry. Highly durable for outdoor landscaping.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was formed in, remaining as resistant ridges or 'monadnocks' long after softer surrounding rocks have eroded away.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its tendency to break across sand grains rather than around them, unlike sandstone. Common in fold mountain belts.
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