metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White to grey, sometimes reddish or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White to grey, sometimes reddish or tan due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White to grey, sometimes reddish or tan due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. It is found in mountain belts worldwide across various geological ages.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative stone in architecture (slabs and tiles), and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often forms the peaks of mountain ranges because it resists weathering better than surrounding rocks. Unlike sandstone, when quartzite is broken, it fractures through the sand grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and stainless steel) and its granular, sugary texture. Look for it in glaciated areas or mountainous terrain where metamorphic rocks are exposed.
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