metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, with yellow, green, or reddish staining from iron oxides or organic material; Luster: vitreous to waxy; Texture: grainy but interlocked crystals; specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, with yellow, green, or reddish staining from iron oxides or organic material; Luster: vitreous to waxy; Texture: grainy but interlocked crystals; specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together into a dense, hard rock. This specimen shows signs of fluvial erosion (river rounding).
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and roofing granules. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so tough that it often survives intense weathering that breaks down other rocks. It is harder than steel and will easily scratch a glass bottle or a knife blade.
Field identification & locations
Identify by its extreme hardness and lack of reaction to acid. In the field, look for a sugary or crystalized appearance on fresh breaks. This specific piece is a river-tumbled cobble often found in gravel beds or glacial till.
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