metamorphic
Quartzite Pebble
Metamorphic Quartz-rich Rock (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with dark secondary mineral band; Luster: Vitreous to dull (tumble-polished by water); Crystal Structure: Hexagonal (microcrystalline); Cleavage: None/Conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with dark secondary mineral band
- Luster
- Vitreous to dull (tumble-polished by water)
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with dark secondary mineral band; Luster: Vitreous to dull (tumble-polished by water); Crystal Structure: Hexagonal (microcrystalline); Cleavage: None/Conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure causes recrystallization of the quartz grains, making it much harder than the original sedimentary rock. This specific specimen has been rounded by fluvial or beach erosion.
Uses & applications
Common quartzite is used in construction as road ballast and railway ballast. Polished pebbles are used in landscaping, floral arrangements, and decorative garden paths.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges. It is harder than steel and will easily scratch a knife blade.
Field identification & locations
Identify by its hardness (it will scratch glass) and lack of reaction to acid. Commonly found on beaches, riverbeds, and glacial till. Collectors look for unique banding patterns like the dark stripe seen here.
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