metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically yellowish-brown (stained by iron oxides as seen), white, or gray; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically yellowish-brown (stained by iron oxides as seen), white, or gray; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz sandstone under intense heat and pressure. The individual quartz grains recrystallize into a locked mosaic of crystals.
Uses & applications
Used in construction as a decorative stone, railway ballast, and in the manufacturing of glass and ceramics. Sometimes ground for industrial sand.
Geological facts
Quartzite is so tough that it often outlasts other rocks during erosion, creating prominent ridges and hills. It is harder and more durable than the parent sandstone from which it originated.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in riverbeds as rounded cobbles or along mountain belts.
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