sedimentary

Yellow Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Yellow to tan, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified May 22, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Yellow to tan, Luster: Waxy to dull, Crystal structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & geological history

Forms through the precipitation of silica-rich fluids within sedimentary rock layers, often replacing organic material or occupying voids. It is typically found in marine environments ranging from the Paleozoic to the Cenozoic era.

Uses & applications

Used historically for stone tools and arrowheads due to its conchoidal fracture. Today used as aquarium gravel, in landscaping, and as a semi-precious stone in lapidary work.

Geological facts

Chert was used by early humans to strike fire when hit against steel or iron pyrites. Its yellow color often comes from trace amounts of iron oxides like goethite.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy appearance, and sharp, shell-like (conchoidal) edges when broken. It is extremely common in limestone and chalk deposits globally.