sedimentary
Chert (Yellow or Ochre Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Opaque yellowish-brown to tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Opaque yellowish-brown to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Opaque yellowish-brown to tan; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary basins or the replacement of limestone. This specimen appears water-worn or tumbled, likely from a fluvial (river) environment, dating from various eras depending on the local bedrock.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; modernly used in landscaping, as a minor gemstone (jasper), or as an abrasive.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. Early humans prioritized this material over almost any other for crafting arrowheads and scrapers.
Field identification & locations
Identify in the field by its smooth, waxy texture and inability to be scratched by a steel knife. It will also spark when struck against steel. Commonly found in gravel pits, riverbeds, and as nodules within limestone outcrops.
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