metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with yellow/orange oxidation; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking crystalline grains; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan with yellow/orange oxidation
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan with yellow/orange oxidation; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking crystalline grains; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating a dense, durable rock. These specimens often appear rounded due to water erosion in fluvial environments.
Uses & applications
Used widely in construction as crushed stone for road gravel and railway ballast. Due to its hardness, it is also used for decorative stones, floor tiles, and historically as a source for stone tools.
Geological facts
Quartzite is so hard that when it breaks, the fracture passes through the quartz grains rather than along the boundaries between them, unlike its precursor sandstone. It is resistant to chemical weathering.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass or steel) and sugary, crystalline texture on a fresh break. Commonly found in mountain ranges or as river-worn cobbles in sedimentary basins.
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