metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow with iron staining; Luster: vitreous to dull; Crystal structure: hexagonal/microcrystalline; Cleavage: none; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or yellow with iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or yellow with iron staining; Luster: vitreous to dull; Crystal structure: hexagonal/microcrystalline; Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Quartzite is a non-foliated metamorphic rock that forms when quartz-rich sandstone is subjected to heat, pressure, and chemical activity. These conditions recrystallize the sand grains and the silica cement that binds them together. Most formations date back to the Proterozoic or Paleozoic eras.
Uses & applications
Used in construction for road ballast and aggregate, as a decorative stone in countertops and floor tiles, and historically as a tool stone for making scrapers and points.
Geological facts
Quartzite is so hard that it can easily scratch glass. It is often confused with marble, but can be distinguished because marble will react (fizz) with acid, whereas quartzite will not.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a steel blade) and its sugary, crystalline texture on a fresh break. Commonly found in mountain ranges or as water-worn cobbles in riverbeds and on beaches.
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