metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish due to iron oxides; Luster: vitreous to dull; Crystal Structure: non-foliated granoblastic; Cleavage: none (fractures across 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, gray, or tan but can be reddish due to iron oxides; Luster: vitreous to dull; Crystal Structure: non-foliated granoblastic; Cleavage: none (fractures across grains); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartzose sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together. It can range in geological age from Precambrian to Cenozoic.
Uses & applications
Used in construction as a decorative stone, crushed stone for road aggregates and railway ballast, and in the production of glass and industrial abrasives. It is also a source of silica for metal smelting.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the caps of ridges and mountains. It is often confused with marble, but marble can be scratched by a steel blade, whereas quartzite cannot.
Field identification & locations
Identify in the field by its extreme hardness (will scratch glass) and its sugary, crystalline texture. Unlike sandstone, which breaks around the sand grains, quartzite breaks directly through the silica grains. Common in mountainous regions and shield areas globally.
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