metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or red due to iron oxides; Luster: vitreous (glassy); Crystal structure: trigonal (hexagonal) through recrystallization; Cleavage: none, breaks with a conchoidal or irregular fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy)
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or red due to iron oxides; Luster: vitreous (glassy); Crystal structure: trigonal (hexagonal) through recrystallization; Cleavage: none, breaks with a conchoidal or irregular fracture.
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure during regional or contact metamorphism, causing the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in the construction industry as crushed stone for road gravel and rail ballast, as building stone (facades and flooring), and in the manufacture of glass and silica-based products.
Geological facts
Quartzite is often even harder and more durable than the parent sandstone it originated from; it is so tough that it often forms the resistant caps of many high ridges and mountain ranges.
Field identification & locations
Identify by its hardness (will scratch glass easily) and its sugary, granular appearance that doesn't rub off like sandstone; frequently found in folded mountain belts.
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