metamorphic
Quartzite
Quartzite (chiefly SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogenic processes). The original quartz grains recrystallize into a tight interlocking mosaic.
Uses & applications
Used as a decorative stone in construction, flooring, countertops, railway ballast, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it forms in, creating prominent ridges. It is often confused with marble but can be distinguished because quartzite will scratch glass and marble will not.
Field identification & locations
Identify in the field by its extreme hardness and granular, sugary appearance. It will not fizz with acid. Found globally in ancient metamorphic terrains, particularly in the Appalachians and Precambrian shields.
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