metamorphic
Quartzite (tumbled or water-worn)
Quartzite (composition: SiO2)
Hardness: 7 (Mohs scale); Color: Pinkish-brown or tan; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Pinkish-brown or tan
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Pinkish-brown or tan; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone under high heat and pressure, causing recrystallization of sand grains into an interlocking mosaic. Found in various geological ages ranging from Precambrian to more recent tectonic mountain-building events.
Uses & applications
Used widely as crushed stone for road construction, railway ballast, and decorative landscaping. High-purity quartzite is used in the manufacturing of glass and silicon carbide.
Geological facts
Quartzite is so durable that it often survives intense weathering better than the surrounding rock, frequently forming the peaks of ridges and mountains. It is substantially harder and more durable than the parent sandstone from which it originated.
Field identification & locations
Identify in the field by its extreme hardness (will scratch glass easily) and its sugary, crystalline texture when broken. It is commonly found in riverbeds as rounded 'creek stones' or in mountain ranges. Collectors look for pieces with unique banding or high transparency.
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