sedimentary

Chert (Jasper)

Cryptocrystalline Silica (SiO2)

Hardness: 7 Mohs scale; Color: Reddish-brown, tan, and dark brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.5–2.8

Hardness: 7 Mohs scale
Color: Reddish-brown, tan, and dark brown
Luster: Waxy to dull

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Reddish-brown, tan, and dark brown; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.5–2.8

Formation & geological history

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolaria) or through chemical precipitation in sedimentary basins. This type of jasper/chert can range from hundreds of millions of years old based on the local formation.

Uses & applications

Used historically for stone tools and arrowheads; currently used in jewelry (cabochons), lapidary art, and as decorative landscape stone.

Geological facts

Chert and jasper have been used by humans for over 2 million years to create sharp-edged tools due to their predictable conchoidal fracture pattern. Yellow and brown hues are often caused by iron inclusions (goethite/limonite).

Field identification & locations

Identified by its high hardness (scratches glass), waxy luster when wet or polished, and smooth, curved (conchoidal) fracture surfaces. Commonly found in riverbeds, glacial till, and sedimentary outcrops worldwide.