metamorphic
Quartzite
Quartzite (composed primarily of Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: white, gray, or tan; Luster: vitreous or sugary; Structure: granular/crystalline texture; Cleavage: none (conchoidal fracture).
- Hardness
- 7 (Mohs scale)
- Color
- white, gray, or tan
- Luster
- vitreous or sugary
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Physical properties
Hardness: 7 (Mohs scale); Color: white, gray, or tan; Luster: vitreous or sugary; Structure: granular/crystalline texture; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional or contact metamorphism. This recrystallizes the quartz grains into a dense, interlocking mosaic.
Uses & applications
Used in construction as crushed stone, road ballast, and decorative stone. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks; it commonly forms the crests of mountain ranges and resistant ridges. It is often confused with marble but can be distinguished by its superior hardness.
Field identification & locations
Identify in the field by its ability to scratch glass and its granular, sandpaper-like appearance that does not fizz with acid. It is commonly found in mountain belts and river beds as rounded cobbles like this specimen.
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