metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grainy, sandpaper-like surface feel; Conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray; Luster: vitreous to dull; Crystal structure: hexagonal (trigonal); Grainy, sandpaper-like surface feel; Conchoidal fracture.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, causing quartz grains to recrystallize and fuse together. Typically found in mountain belts formed by plate tectonics.
Uses & applications
Used as crushed stone for road construction, as dimension stone for counter tops and flooring, and occasionally as a gemstone or in glass making.
Geological facts
Quartzite is so hard that it can scratch glass and steel. It is often confused with marble, but unlike marble which reacts with acid, quartzite is chemically stable and durable.
Field identification & locations
Identify in the field by its superior hardness and lack of reaction to hydrochloric acid. Common in riverbeds as rounded pebbles or in mountainous outcrops.
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