metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White to grey, with possible reddish or yellow tints due to impurities. Luster: Vitreous to dull. Crystal structure: None (granular/macrocrystalline). Cleavage: None; displays conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White to grey, with possible reddish or yellow tints due to impurities. Luster: Vitreous to dull. Crystal structure: None (granular/macrocrystalline). Cleavage: None; displays conchoidal fracture.
Formation & geological history
Formed from the metamorphism of quartz sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together, creating a hard, dense masonry. It can range in age from Precambrian to more recent geological eras depending on location.
Uses & applications
Used extensively in construction for road ballast, floor tiles, and countertop surfaces. Also used as decorative stone in landscaping and sometimes as a source for silica in glass production.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the peaks of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary appearance on fresh surfaces. It is found globally in mountain-building regions.
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