metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored yellow, orange, or red by iron oxides; Luster: Vitreous/waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous/waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often colored yellow, orange, or red by iron oxides; Luster: Vitreous/waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with a conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure from tectonic activity, the quartz grains recrystallize and fuse together into a dense, hard industrial rock.
Uses & applications
Used in construction as road ballast, roofing granules, and Dimension stone. Polished specimens are used in jewelry (as agates/jaspers) and ornamental landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain-building events, frequently forming the peaks of ridges and mountains. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify by its ability to scratch glass and its grainy, sugary appearance on fresh surfaces despite being very hard. Commonly found in riverbeds and mountainous glacial tills.
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