metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, but often brown or reddish from iron oxide staining; Luster: vitreous to dull; Crystal Structure: non-foliated, interlocking quartz grains; 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 grey, but often brown or reddish from iron oxide staining; Luster: vitreous to dull; Crystal Structure: non-foliated, interlocking quartz grains; specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Formed in orogenic (mountain-building) belts throughout various geological eons from the Proterozoic to more recent times.
Uses & applications
Used in construction as road ballast, railway ballast, and building stone. Highly decorative varieties are used for kitchen countertops and floor tiles. Crushed quartzite is used as a source of silica in glass manufacturing.
Geological facts
Quartzite is so durable that it often forms the capstones and ridges of mountains because it resists erosion better than the surrounding rock. It is often mistaken for marble, but can be distinguished by its superior hardness (marble is scratched by steel, quartzite is not).
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass) and its grainy, crystalline texture that breaks through the grains rather than around them. Common in river beds and glaciated areas as rounded cobbles.
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