sedimentary
Chert (Beach Pebble)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: light grey to cream; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs scale)
- Color
- light grey to cream
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: light grey to cream; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the precipitation of microcrystalline silica in marine environments or by the replacement of calcium carbonate in limestone. These pebbles are often tumbled smooth by wave action over thousands of years.
Uses & applications
Historically used for stone tools/arrowheads. Modernly used in landscaping, as a construction aggregate, and occasionally tumbled for jewelry or pocket stones.
Geological facts
Chert specifically formed in marine environments often contains microscopic fossil remains. It is chemically identical to quartz but has a much finer-grained structure.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and smooth, rounded shape if found on a beach. It often has a waxy feel when handle.
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