metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale. Color: White to light grey (sometimes pink or red due to iron). Luster: Vitreous/Glassy to waxy. Crystal structure: Trigonal (granular texture). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to light grey (sometimes pink or red due to iron)
- Luster
- Vitreous/Glassy to waxy
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Physical properties
Hardness: 7 on Mohs scale. Color: White to light grey (sometimes pink or red due to iron). Luster: Vitreous/Glassy to waxy. Crystal structure: Trigonal (granular texture). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic compression cause the sand grains to recrystallize and fuse together. Typically found in mountain belts and Precambrian shields.
Uses & applications
Used in construction as road ballast, roofing granules, and decorative stone. Sometimes used for countertops, though less common than granite. Historically used for making stone tools.
Geological facts
Quartzite is so tough that it often survives erosion better than other rocks, forming prominent ridges or hilltops. It can be distinguished from marble because it will not react (fizz) with acid and is much harder.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and granular, sugary appearance. It is commonly found in riverbeds as rounded cobbles or in massive outcrops in metamorphic terrains.
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