metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Brownish-orange to tan due to iron oxide staining; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Brownish-orange to tan due to iron oxide staining
- Luster
- Vitreous to waxy when polished
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Physical properties
Hardness: 7 (Mohs scale); Color: Brownish-orange to tan due to iron oxide staining; Luster: Vitreous to waxy when polished; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize and fuse together. The rounded shape indicates significant water erosion, likely in a river or glacial environment.
Uses & applications
Used primarily as decorative gravel in landscaping, as an abrasive, and sometimes in construction as a sturdy road aggregate. Tumbled specimens are used in lapidary work.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during weathering, leaving behind these resistant pebbles. It is one of the hardest common rocks found at the Earth's surface.
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass) and its sugary texture under a lens. Found globally in riverbeds, beaches, and glacial till. Common in areas with old mountain belts.
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