metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can have yellowish tints; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, can have yellowish tints
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can have yellowish tints; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize and fuse into a dense rock.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a raw material in the manufacturing of glass and ceramics. High-quality slabs are used for countertops and floor tiles.
Geological facts
Quartzite is so tough that it often survives intense weathering better than the rocks around it, leading it to form prominent ridges and mountain peaks. It is often confused with marble, but quartzite is much harder and will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and lack of reaction to hydrochloric acid. Look for a sugary, granular texture that looks like fused sand. Frequently found in riverbeds as rounded 'river rocks' due to its durability.
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