metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create yellow and orange tints as seen here; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create yellow and orange tints as seen here; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, hard rock. This specimen appears to be part of a river bed or glacial deposit.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping. In its purest form, it is used to produce glass and industrial silica.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, forming prominent ridges or peaks. 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 (cannot be scratched by a steel nail) and the way it breaks across the grains rather than around them. Commonly found in folded mountain belts and ancient cratons.
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