metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create yellow and brown tones (as seen in the image); Luster: vitreous to waxy; Structure: granular, non-foliated crystalline; Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities create yellow and brown tones (as seen in the image); Luster: vitreous to waxy; Structure: granular, non-foliated crystalline; Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Intense heat and pressure cause the original quartz grains to recrystallize and fuse together, creating a much harder rock. Most deposits date from the Proterozoic to Phanerozoic eons.
Uses & applications
Used extensively in construction as road ballast and building stone. Highly valued for countertops (under the name 'granite' or 'natural stone') due to its hardness and resistance to acids. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in weathering, leading to the formation of prominent ridges and peaks. It is often confused with marble, but can be distinguished by its ability to scratch glass and its lack of reaction to acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its sugary, crystalline texture on fresh breaks. It is found globally, with massive deposits in the Appalachians, Brazil, and Scandinavia. Look for its characteristic lack of bubbles when exposed to vinegar.
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