metamorphic
Quartzite
Quartzite (Silicon Dioxide: SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none; 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, gray, or tan, but often yellow or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism. This causes the individual sand grains to recrystallize into an interlocking mosaic of quartz crystals. It can date back from the Precambrian to recent periods.
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. In industry, it is a source of silica for glassmaking and metal smelting. Sometimes used for decorative landscaping and as dimension stone.
Geological facts
Quartzite is so strong that when it breaks, it fractures through the sand grains rather than around 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 extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a sugary, crystalline appearance on fresh surfaces. Commonly found in folded mountain belts globally.
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