metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or brownish iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal 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, often with yellow or brownish iron staining; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking mosaic. It can be found in mountain belts and Precambrian shields globally.
Uses & applications
Used as a decorative stone in architecture, a source of silica for glass making, railway ballast, and in the production of ferro-silicon. High-quality pieces are used for countertops and flooring.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, frequently forming the crests of ridges and mountain peaks. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify by its extreme hardness and its sugary, granular texture when viewed closely. Unlike marble (which it resembles), it will not fizz when exposed to acid. Commonly found in riverbeds as rounded cobbles or in mountainous outcrops.
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