sedimentary
Chert (Yellow Jasper variant)
Microcrystalline Quartz (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Dull yellow to mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
- Hardness
- 6
- Color
- Dull yellow to mustard
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Dull yellow to mustard; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
Formation & geological history
Formed from the precipitation of silica-rich fluids in sedimentary environments, often as nodules or beds within limestone or chalk. Many specimens date from the Paleozoic or Mesozoic eras.
Uses & applications
Used historically for stone tools and arrowheads due to conchoidal fracturing; used today for lapidary work, jewelry, and as a component in road construction or decorative landscaping.
Geological facts
Chert was one of the most important minerals for early humans because its sharp edges when broken were superior for cutting and scraping tools. Yellow variants often get their color from goethite or limonite inclusions.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy texture, and curved, shell-like (conchoidal) fractures. Found worldwide in sedimentary basins, riverbeds, and coastal cliffs.
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