metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or tan with iron staining; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or tan with iron staining
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or tan with iron staining; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic plate collisions. Most quartzite originates from Precambrian or Paleozoic eras.
Uses & applications
Used in construction as road ballast, gravel, and dimension stone; also used as a source of silica for glass making and as decorative garden stone.
Geological facts
Quartzite is so hard and durable that it often forms the tops of ridges and mountains because it resists weathering better than the surrounding rock. It is harder than a steel knife and will scratch glass easily.
Field identification & locations
Identify in the field by its sugary, granular texture and its inability to be scratched by a steel blade. Common in ancient mountain belts like the Appalachians or the Scottish Highlands.
