sedimentary

Chert (Yellow Jasper variant)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified April 12, 2026More sedimentary →

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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.