metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but varies into purple, pink, or red depending on impurities (like iron); Luster: vitreous to waxy; Texture: granular, crystalline; Cleavage: none; Specific Gravity: 2.6–2.65
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but varies into purple, pink, or red depending on impurities (like iron); Luster: vitreous to waxy; Texture: granular, crystalline; Cleavage: none; Specific Gravity: 2.6–2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a solid, sugary-textured mass. The age varies based on the parent sandstone, often dating back hundreds of millions of years (Proterozoic to Paleozoic era).
Uses & applications
Used widely in construction as decorative stone, crushed stone for road bases, and ballast for railways. High-purity quartzite is used in the metallurgical and chemical industries to produce silicon metal and glass.
Geological facts
Quartzite is so tough that it usually breaks straight through the quartz grains rather than along the boundaries between them. It is one of the most resistant rocks on Earth's surface, often forming the resistant caps of mountain ridges.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a steel nail) and its sugary, sparky surface where individual quartz grains have fused. Commonly found in mountainous regions such as the Appalachians, Salt Lake City area, and parts of the UK.
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