metamorphic
Quartzite
Metamorphic Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: white to yellowish-orange due to iron staining; Luster: vitreous to grainy; Crystal structure: Trigonal (granular texture); Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- white to yellowish-orange due to iron staining
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: white to yellowish-orange due to iron staining; Luster: vitreous to grainy; Crystal structure: Trigonal (granular texture); Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to intense heat and pressure during regional metamorphism. This process recrystallizes the sand grains into a tightly interlocking network of quartz crystals.
Uses & applications
Used extensively in construction as crushed stone for road building, as dimension stone for flooring and countertops, and occasionally in glassmaking if the silica content is high enough.
Geological facts
Quartzite is so tough that it often outlasts surrounding rocks; many hills and ridges in old mountain ranges are capped with quartzite because it is highly resistant to chemical and physical weathering.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and the fact that it breaks through the sand grains rather than around them, unlike sandstone. Common in mountain belts globally.
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