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 vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Dull yellow to mustard
Luster: Waxy to vitreous

Identified May 27, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Dull yellow to mustard; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed via the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Can be found in rocks from Precambrian to Holocene eras.

Uses & applications

Historically used for stone tools and arrowheads; currently used in jewelry (cabochons), as an abrasive, and by crystal collectors.

Geological facts

Chert is so hard it can create sparks when struck against steel, which made it vital for flintlock firearms and early fire-starting tools.

Field identification & locations

Identify in the field by its characteristic smooth, curved (conchoidal) fracture surfaces and its ability to scratch glass. Found globally in limestone and dolomite beds or as stream pebbles.