metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to grainy; Crystal structure: Trigonal; Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to grainy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to grainy; Crystal structure: Trigonal; Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events in tectonic plate boundaries.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, as railroad ballast, and sometimes in glass manufacturing if the quartz content is high enough.
Geological facts
Quartzite is so tough that it often outlasts other rocks in its environment, forming ridge-tops and high mountain crests. It is harder than steel and will scratch a glass plate.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will not be scratched by a knife). Commonly found in folded mountain belts globally like the Appalachians or Alps.
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