metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, with pink/red tints from iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; Specific gravity: approx. 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, with pink/red tints from iron oxide
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, with pink/red tints from iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; Specific gravity: approx. 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. Specimens like this are often rounded due to river or glacial erosion.
Uses & applications
Used widely in construction as crushed stone for road grit and railway ballast. High-purity quartzite is used to produce glass and silica for industrial chemistry. Polished specimens are used as decorative stones or in landscaping.
Geological facts
Quartzite is so tough that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone. It is one of the most durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. It is commonly found in mountain ranges and glacial till across North America and Europe.
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