metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (iron inclusions can cause yellow/brown); Luster: vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: none, breaks with conchoidal or irregular 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, gray, or tan (iron inclusions can cause yellow/brown); Luster: vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: none, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.65
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, obliterating the original grain boundaries. Geological age can range from Precambrian to Cenozoic.
Uses & applications
Used widely in construction as crushed stone for road gravel and railroad ballast. High-purity quartzite is used in the manufacture of glass and silicon. Polished stones are used for decorative landscaping and interior flooring.
Geological facts
Quartzite is so durable that it can withstand intense weathering; it often forms prominent ridges and peaks in mountain ranges. It is often distinguished from sandstone because it breaks across the grains rather than around them.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and its sugary/crystalline texture that lacks the visible pore spaces of sandstone. Found globally, especially in mountain belts like the Appalachians or Alps. Collectors look for unique colors or surface textures.
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