metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high pressure and temperature, individual quartz grains recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, in the manufacture of glass and ceramics, and as a durable material for kitchen countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the resistant caps of ridges and mountains; unlike sandstone, it will break through the quartz grains rather than around them.
Field identification & locations
Identify by its extreme hardness (scratches glass/steel) and its sugary, crystalline texture. It is commonly found in fold mountain belts globally. For collectors, look for pieces with interesting color banding or crystal inclusions.
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