metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to grainy; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white to light gray
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: white to light gray; Luster: vitreous to grainy; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone subjected to high heat and pressure, typically found in orogenic (mountain-building) belts. Age varies by tectonic setting.
Uses & applications
Used extensively in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is used to produce ferrosilicon and industrial sand.
Geological facts
Quartzite is so hard that it can easily scratch glass and steel. It often forms the resistant caps of many mountain ridges and peaks because it is highly resistant to chemical and physical weathering.
Field identification & locations
Identify in the field by its superior hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like surface that lacks distinctive layering. Common in the Appalachian Mountains and the Brazilian Shield.
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