metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron can create pink/red hues); Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (conchoidal 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, gray, or tan (iron can create pink/red hues); Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used widely in construction as decorative stone, crushed stone for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is also used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the crests of ridges and resistant hilltops. It is virtually insoluble and doesn't react with acid, unlike marble.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its granular, sugary texture. Unlike sandstone, it breaks across the quartz grains rather than around them. Common in folded mountain belts globally.
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