metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, grey, and tan with dark mineral bands; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white, grey, and tan with dark mineral bands
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, grey, and tan with dark mineral bands; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic plate collisions and mountain-building events.
Uses & applications
Used extensively in road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so durable that it often survives intense weathering that destroys other rocks, leading it to form prominent ridges and mountain peaks. It is often harder than the steel tools used to mine it.
Field identification & locations
Identified in the field by its sugary, granular texture and inability to be scratched by a steel pocketknife. Commonly found in riverbeds as rounded cobbles due to its extreme resistance to erosion.
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