sedimentary
Chert (specifically Tan/Yellow Chert)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or pale yellow; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or pale yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or pale yellow; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in limestone/chalk environments. This piece appears to be a stream-tumbled or weathered nodule fragment.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as road surfacing material, in high-wear ceramics, or as a decorative landscaping stone.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital materials for prehistoric humans for survival tools. Its cryptocrystalline structure means the quartz crystals are so small they can only be seen under extreme magnification.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to spark when struck against steel. Commonly found in riverbeds, glacial till, or embedded within limestone outcrops. For collectors, look for pieces with unique color banding or fossil inclusions.
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