metamorphic
Quartzite
Quartzite (composed primarily of SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-pink to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Reddish-pink to light grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-pink to light grey; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure. The reddish hue is typically due to iron oxide impurities (hematite). Many specimens in glacial areas originate from the Precambrian era.
Uses & applications
Used in construction as a decorative stone, road ballast, railway ballast, and crushed stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial silicon.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming ridges and resistant outcrops. It is one of the hardest and most chemically resistant rocks on Earth's surface.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture. Look for it in glacial till or mountainous metamorphic belts. Unlike limestone, it will not fizz with acid.
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