metamorphic
Quartzite (River Pebble)
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan or peach; Luster: Vitreous when wet or polished; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan or peach
- Luster
- Vitreous when wet or polished
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan or peach; Luster: Vitreous when wet or polished; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Quartzite forms through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. The rounded shape indicates it was later eroded and tumbled by water in a river or coastal environment.
Uses & applications
Used in construction as road ballast, decorative masonry, and landscaping stone. Larger, colorful pieces are sometimes used in lapidary work for cabochons or tumbled stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, leading to the formation of prominent ridges and peaks. It is often confused with marble, but can be distinguished by its inability to be scratched by a steel knife.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and lack of visible grains compared to regular sandstone. Common in ancient sedimentary basins and riverbeds globally. Collectors look for unique colors or high translucent quality.
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