metamorphic
Quartzite (River Pebble)
Metamorphosed Quartz Sandstone (primarily SiO2)
Hardness: 7 (Mohs scale); Color: Off-white/tan with pinkish-orange iron staining; Luster: Dull/Waxy (weathered) to Vitreous (internal); Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Off-white/tan with pinkish-orange iron staining
- Luster
- Dull/Waxy (weathered) to Vitreous (internal)
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Physical properties
Hardness: 7 (Mohs scale); Color: Off-white/tan with pinkish-orange iron staining; Luster: Dull/Waxy (weathered) to Vitreous (internal); Structure: Non-foliated, granular; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the metamorphism of pure quartz sandstone under intense heat and pressure. The sandstone recrystallizes into a hard, interlocking mosaic of quartz crystals. This specimen has been rounded by fluvial chemical and physical erosion (river transport).
Uses & applications
Commonly used in construction as crushed stone for road gravel and rail ballast. High-purity quartzite is used in glassmaking. Polished stones (river rocks) are used in landscaping and interior design.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of massive mountain ranges (resistant ridges). It will scratch glass easily, which distinguishes it from softer stones like marble or limestone.
Field identification & locations
Identify in the field by its sugary/granular appearance and extreme hardness (cannot be scratched by a steel knife). Commonly found in riverbeds, glacial tills, and ancient mountain belts. Collectors look for unique iron-oxide bands known as 'desert varnish' or internal mineralization.
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