metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish tints; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, and reddish tints
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, and reddish tints; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing quartz grains to recrystallize and fuse together. Typically found in Appalachian or Alpine-type mountain belts.
Uses & applications
Used as a decorative stone in construction, counter tops, railroad ballast, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard that it can scratch steel. When broken, quartzite fractures across its constituent quartz grains rather than around them, unlike its parent rock sandstone.
Field identification & locations
Identify by its extreme hardness and granular, sugary appearance. Found globally in ancient tectonic zones. Collectors look for unique color bands or embedded mineralization.
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