metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or pink tints; Luster: vitreous to grainy; Crystal structure: hexagonal (microcrystalline); specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, often with yellow or pink tints
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or pink tints; Luster: vitreous to grainy; Crystal structure: hexagonal (microcrystalline); specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. It occurs when sandstone is subjected to intense heat and pressure, causing the original quartz grains to recrystallize and fuse together into a dense, interlocking matrix.
Uses & applications
Used as crushed stone for road construction and railway ballast; flat slabs are used in flooring and wall coverings; varieties with high purity are used to produce silicon and glass.
Geological facts
Quartzite is so tough that it often survives the weathering process better than surrounding rocks, forming prominent ridges and hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it cannot be scratched by a steel nail). It breaks across grains rather than around them, unlike its parent rock sandstone. Found globally in ancient mountain belts.
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