metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan to yellow-brown (due to iron oxide staining); Luster: Vitreous to dull; Crystal structure: Granular/Massive; Cleavage: None (conchoidal to uneven fracture).
- Hardness
- 7 on Mohs scale
- Color
- Tan to yellow-brown (due to iron oxide staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan to yellow-brown (due to iron oxide staining); Luster: Vitreous to dull; Crystal structure: Granular/Massive; Cleavage: None (conchoidal to uneven fracture).
Formation & geological history
Quartzite forms when quartz-rich sandstone is subjected to intense heat and pressure (metamorphism). The sand grains recrystallize and fuse together, creating a much harder rock. This example appears to be a water-worn river cobble.
Uses & applications
Used extensively in road construction (as riprap or crushed stone), as a decorative stone in landscaping, and in glass manufacturing if the quartz purity is very high.
Geological facts
Quartzite is so tough that it often survives erosion better than the surrounding rock, frequently forming the tops of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its hardness (7) and the way it breaks through the sand grains rather than around them like sandstone. Common in mountainous regions or as river-transported cobbles.
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