sedimentary
Beach Pebble (Chert/Quartzite)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or milky beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Gray, tan, or milky beige
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or milky beige; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the precipitation of silica in sedimentary environments or the metamorphism of quartz-rich sandstone. These specific specimens have been water-worn and smoothed by wave action in a coastal or riverine environment over thousands of years.
Uses & applications
Used primarily as decorative landscaping gravel, in construction as aggregate, or as low-cost pocket stones for amateur collectors. Higher-grade varieties like jasper or flint are used for lapidary work.
Geological facts
Chert was historically significant as one of the primary materials used by prehistoric humans to create tools and arrowheads due to its predictable conchoidal fracturing. Small beach pebbles like these are often referred to as 'pocket stones.'
Field identification & locations
Identify in the field by their smooth, rounded shape and ability to scratch glass. They are commonly found on shorelines, riverbeds, and in glacial till throughout the world. Collectors look for unique banding or translucency.
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