metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; 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). These specimens can range in age from hundreds of millions to billions of years old.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the tops of ridges and mountains. It is significantly harder and more durable than the sandstone it originated from.
Field identification & locations
Identify in the field by its ability to scratch glass and its grainy, sandpaper-like texture (though smooth when water-worn). Unlike marble, it will not fizz with acid. Often found in riverbeds as rounded pebbles or on mountain slopes.
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