metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on the Mohs scale. Color: Commonly white, gray, or tan (as seen in the specimen). Luster: Vitreous to dull. Structure: Granoblastic, non-foliated. Cleavage: Indistinct/Conchoidal fracture.
- Hardness
- 7 on the Mohs scale
- Color
- Commonly white, gray, or tan (as seen in the specimen)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Commonly white, gray, or tan (as seen in the specimen). Luster: Vitreous to dull. Structure: Granoblastic, non-foliated. Cleavage: Indistinct/Conchoidal fracture.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together, creating a dense, interlocking matrix. Usually associated with Precambrian or Paleozoic formations.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is used in the glass and chemical industries to produce silicon products.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, forming prominent ridges and hills (monadnocks). It is often mistaken for marble but can be distinguished because it will not react with acid and cannot be scratched by a steel blade.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (will scratch glass). It typically breaks across the quartz grains rather than around them. Found globally in mountainous regions like the Appalachians (USA) or the Alps.
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