metamorphic
Quartzite (with Iron Staining)
Quartzite (predominantly SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored brown or orange by iron oxides; Luster: Vitreous to dull; Crystal Structure: Granular/Massive; SG: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored brown or orange by iron oxides; Luster: Vitreous to dull; Crystal Structure: Granular/Massive; SG: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together. These rocks can range from Precambrian to much younger geological ages.
Uses & applications
Used primarily in construction for crushed stone, road ballast, and ornamental building stone. High-purity quartzite is used in the glass industry and to produce silicon and ferrosilicon.
Geological facts
Quartzite is so tough and resistant to chemical weathering that it often forms the ridges of mountain ranges. It is much harder than sandstone; if you hit it with a hammer, it will break through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass) and its granular, sugary texture. Common in Appalachian and Rocky Mountain orogenies. Look for an absence of reaction with acid to distinguish from marble.
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