metamorphic
Quartzite
Metamorphic Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan, cream, or white with reddish stains from iron; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (fractures conchoidally); Specific gravity: 2.63 - 2.65
- Color
- tan, cream, or white with reddish stains from iron
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, cream, or white with reddish stains from iron; Luster: vitreous to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none (fractures conchoidally); Specific gravity: 2.63 - 2.65
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, hard rock. Found in mountain belts and areas with ancient continental crust.
Uses & applications
Used widely as road ballast, construction aggregate, and in dimension stone for flooring and countertops. Historically used for stone tools due to its hardness and sharp conchoidal fracture.
Geological facts
Quartzite is so hard that it will scratch glass and steel. It is much more resistant to chemical weathering than other rocks, which is why it often forms the resistant ridges and peaks of mountain ranges.
Field identification & locations
Identify in the field by its hardness (will scratch a knife blade) and its grainy, sandpaper-like texture that has been fused so smooth it looks like glass. Common in riverbeds as rounded cobbles like the one pictured.
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