metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None, breaks with conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to light gray
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None, breaks with 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, the individual quartz grains recrystallize and interlock firmly, creating a non-foliated metamorphic rock.
Uses & applications
Used in construction for road ballast, roofing granules, and as a decorative stone in landscaping and flooring. High-purity quartzite is also used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough and resistant to chemical weathering that it often forms the tops of ridges and resistant hills known as 'hogbacks.' It is significantly harder than the sandstone it originates from.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife (unlike marble) and its granular, sugary appearance. It will not react with acid. Common in mountain ranges and ancient shields.
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