metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink/red due to iron oxide; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.63–2.65
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, but pink/red due to iron oxide
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink/red due to iron oxide; Luster: vitreous to dull; Crystal structure: trigonal (granular texture); Cleavage: none; Specific gravity: 2.63–2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). Most quartzite is Proterozoic to Paleozoic in age.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and as a decorative stone in landscaping. High-purity quartzite is a source of silica for glassmaking and silicon production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it weathers much more slowly than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in metamorphic terranes and as water-worn cobbles in riverbeds.
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