metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 on the Mohs scale. Color: White, gray, yellowish, or reddish depending on impurities. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline intergrown quartz crystals). Cleavage: None (fractures conchoidally). Specific gravity: 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- White, gray, yellowish, or reddish depending on impurities
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 on the Mohs scale. Color: White, gray, yellowish, or reddish depending on impurities. Luster: Vitreous to greasy. Crystal structure: Trigonal (microcrystalline intergrown quartz crystals). Cleavage: None (fractures conchoidally). Specific gravity: 2.65.
Formation & geological history
Formed from quartz-rich sandstone under high heat and pressure tectonic processes, typically occurring in mountain-building belts over millions of years.
Uses & applications
Used in construction, railroad ballast, manufacturing of silica brick, decorative landscaping, and occasionally for countertops and monuments.
Geological facts
Because quartz is extremely resistant to weathering, quartzite ridges often form prominent, rugged mountain crests and resistant hills.
Field identification & locations
Identified by its great hardness (scratches glass, cannot be scratched by a knife), lack of reaction to hydrochloric acid, and the way it breaks across the quartz grains rather than around them like sandstone. Found worldwide.
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