sedimentary
Chert (often called Jasper or River Siltstone)
Chert (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: tan, gray, and ochre/yellow; Luster: waxy to dull; Structure: microcrystalline quartz; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8
- Hardness
- 6
- Color
- tan, gray, and ochre/yellow
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: tan, gray, and ochre/yellow; Luster: waxy to dull; Structure: microcrystalline quartz; Cleavage: none (conchoidal fracture); Specific gravity: 2.5-2.8
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specific specimen shows stream-rounded water wear reaching back to the Holocene or Pleistocene epochs.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp fracture edges. Today, it is used as decorative landscaping stone, in lapidary work (jewelry), and for tumbling by collectors.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers, resulting in the smooth, rounded 'river pebble' appearance seen here. Varieties containing iron oxides like limonite produce the yellow/brown coloring visible on the tip.
Field identification & locations
Look for a smooth, waxy texture and a conchoidal (shell-like) fracture pattern. It can be found globally in riverbeds, gravel pits, and sedimentary rock outcrops. It will easily scratch glass.
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