sedimentary
Yellow Chert
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Mustard yellow, tan, or ochre. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Mustard yellow, tan, or ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Mustard yellow, tan, or ochre. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. 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 silica-rich fluids within limestone or chalk beds. Often Paleozoic or Mesozoic in age.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Currently used as road aggregate, in landscaping, and as lapidary material for tumbling.
Geological facts
Chert is so durable that it often remains in creek beds long after the surrounding limestone has eroded away. Yellow varieties are frequently colored by goethite or limonite inclusions.
Field identification & locations
Identify by its waxy texture, smooth conchoidal (shell-like) fractures, and the fact that it can scratch glass. Common in river gravels and sedimentary outcrops globally.
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