metamorphic
River Quartz Pitting / Quartzite Pebble
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Vitreous to dull (waxy when smoothed); Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white
- Luster
- Vitreous to dull (waxy when smoothed)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Vitreous to dull (waxy when smoothed); Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, where individual grains recrystallize into a locked mosaic. This specific specimen has been further shaped into a smooth, rounded 'river stone' through mechanical weathering and water erosion over thousands of years.
Uses & applications
Larger deposits are used for railway ballast, road construction, and flooring. Smooth pebbles like this are popular in landscaping, aquarium decor, and as 'worry stones' or craft painting surfaces.
Geological facts
Quartzite is so durable that it often outlasts the surrounding rock, protruding from the earth as ridges. It is often confused with marble, but unlike marble, it will not fizz when exposed to acid and is much harder than a steel knife blade.
Field identification & locations
Identify in the field by its hardness (it should easily scratch glass) and lack of visible grains or pores. Commonly found in riverbeds, glacial tills, and coastal beaches. Collectors should look for unique translucency or internal fractures that catch the light.
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