sedimentary
Yellow Chert or Jasper
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan to yellow-brown; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Crystal Structure: Microcrystalline quartz.
- Hardness
- 6
- Color
- Tan to yellow-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan to yellow-brown; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Crystal Structure: Microcrystalline quartz.
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in sedimentary environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Used historically for stone tools and arrowheads due to its sharp edges when fractured. Today used for lapidary work, jewelry, and as decorative stone.
Geological facts
Chert is so durable that it often survives as smooth pebbles in riverbeds long after the surrounding rock has eroded away. Yellow varieties are often colored by limonite or goethite.
Field identification & locations
Identify by its waxy luster, smoothness, and distinct 'shell-like' conchoidal fractures. Commonly found in riverbeds, gravel pits, and sedimentary rock outcrops.
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