metamorphic
Quartzite (with mineral vein)
Metamorphosed Quartz-rich Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: light gray to pinkish-tan with a dark mineral vein; Luster: dull to vitreous; Crystal structure: Granular/Microcrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- light gray to pinkish-tan with a dark mineral vein
- Luster
- dull to vitreous
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: light gray to pinkish-tan with a dark mineral vein; Luster: dull to vitreous; Crystal structure: Granular/Microcrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the quartz grains to recrystallize and fuse together. The dark vein likely represents a later hydrothermal injection of minerals like mica or tourmaline into a fracture.
Uses & applications
Commonly used in construction as crushed stone for road gravel, railroad ballast, and occasionally as decorative stone or flooring. High-purity quartzite is used to produce glass and silicon.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is often more resistant to weathering than the surrounding rock, leading it to form prominent ridges and hills over millions of years.
Field identification & locations
Identified in the field by its intense hardness and sandy texture that does not rub off. Unlike sandstone, when broken, quartzite fractures through the grains rather than around them. Common in mountainous regions and glacial deposits.
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