metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (reddish/pink due to iron oxide impurities); Luster: vitreous to grainy; Crystal structure: crystalline/equigranular; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (reddish/pink due to iron oxide impurities); Luster: vitreous to grainy; Crystal structure: crystalline/equigranular; Cleavage: none (fractures across grains); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, causing sand grains to recrystallize and fuse together. Often associated with convergent plate boundaries and mountain-building events (Orogeny).
Uses & applications
Used in construction as crushed stone or road ballast, as dimension stone for wall coverings and flooring, and in industrial glass making or as a source of silica.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering processes, forming prominent ridges and peaks. Unlike sandstone, when quartzite is broken, it fractures through the sand grains rather than around them.
Field identification & locations
Identify in the field by its superior hardness (it will easily scratch glass) and its sugary, granular texture that lacks the visible pores of sandstone. Commonly found in the Appalachian Mountains, Lake Superior region, and Brazil.
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