metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray with reddish-brown iron staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- white to light gray with reddish-brown iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray with reddish-brown iron staining; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse into a solid, interlocking network of crystals.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so hard and dense that when struck with a hammer, it will break through the quartz grains rather than around them, unlike its parent rock, sandstone. It is often resistant to chemical weathering.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and sugary/granular appearance. Commonly found in mountainous regions or as rounded river cobbles due to its durability.
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