sedimentary

Chert (Jasper variety)

Chert (SiO2)

Hardness: 7 (Mohs scale); Color: Yellow-ochre with reddish hematite staining; Luster: Dull to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7

Hardness: 7 (Mohs scale)
Color: Yellow-ochre with reddish hematite staining
Luster: Dull to waxy

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or as bedded deposits. Geological age spans from Precambrian to Holocene.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modern uses include decorative gemstones (when polished), aggregate in construction, and as flint for fire-starting.

Geological facts

Chert was one of the first materials used by early humans for tools. Its fracture pattern, called conchoidal, creates razor-sharp edges similar to glass. This specimen shows a mix of limonite (yellow) and hematite (red) impurities.

Field identification & locations

Identify in the field by its hardness (scratches glass), smooth conchoidal fracture surfaces, and lack of visible grains. Found globally in sedimentary basins. Collectors look for unique banding or color patterns.