metamorphic
Quartzite
Quartzite (SiO2)
Mohs hardness: 7. Color: pinkish-red to purple with white crystalline bands. Luster: vitreous to dull. Texture: granular, non-foliated. Breaking pattern: conchoidal or irregular fractures that cut through sand grains rather than around them.
- Hardness
- 7
- Color
- pinkish-red to purple with white crystalline bands
- Luster
- vitreous to dull
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Physical properties
Mohs hardness: 7. Color: pinkish-red to purple with white crystalline bands. Luster: vitreous to dull. Texture: granular, non-foliated. Breaking pattern: conchoidal or irregular fractures that cut through sand grains rather than around them.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse into a solid mass of quartz crystals. Most specimens date back millions to billions of years.
Uses & applications
Used as decorative stone, crushed stone for road construction, railroad ballast, and sometimes in glass manufacturing if pure. Higher quality pieces are used for countertops and tiles.
Geological facts
Quartzite is so tough and resistant to chemical weathering that it often forms the ridges and peaks of mountain ranges. It is significantly harder and more durable than the sandstone it originates from.
Field identification & locations
Identify by its inability to be scratched by a steel knife and its tendency to break across quartz grains rather than around them. Found globally in ancient mountain belts and shield areas like the Canadian Shield or the Appalachians.
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