metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities can make it pink or reddish-brown; Luster: vitreous to dull; Crystal structure: hexagonal (internal) with a granular, sugary texture; Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities can make it pink or reddish-brown; Luster: vitreous to dull; Crystal structure: hexagonal (internal) with a granular, sugary texture; Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the metamorphism of quartz sandstone. High pressure and heat cause individual quartz grains to recrystallize, fusing them into a solid mass of interlocking quartz crystals. It is found in mountain belts and areas of tectonic activity.
Uses & applications
Commonly used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. Durable varieties are used for high-end landscaping and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so durable that it often remains as the caprock of ridges and mountains long after softer sedimentary rocks have eroded away. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is found worldwide in metamorphic shields. For collectors, seek out specimens with unique color banding or those containing small crystals.
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