metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron oxides often tint it yellow, orange, or reddish; Luster: vitreous to dull; Texture: granoblastic (sugary appearance); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron oxides often tint it yellow, orange, or reddish; Luster: vitreous to dull; Texture: granoblastic (sugary appearance); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, interlocking mosaic of crystals. It is found in mountain belts and areas of uplift globally.
Uses & applications
Used as crushed stone for road construction and railway ballast; due to its hardness and resistance to weathering, it is also used for building facades, floor tiles, and as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rocks, frequently forming the peaks of mountain ranges. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary, crystalline texture and extreme hardness (it will not be scratched by a steel blade). Unlike sandstone, when quartzite breaks, it fractures through the quartz grains rather than around them. It is very common in riverbeds as water-worn cobbles.
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