sedimentary

Chert (Cherty Flint/Jasper variety)

Microcrystalline or cryptocrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Tan, brownish-grey, and cream. Luster: Dull to waxy. Crystal Structure: Hexagonal (microcrystalline). Cleavage: None, exhibits prominent conchoidal (shell-like) fracture. Specific Gravity: 2.6 - 2.7.

Hardness: 7 on the Mohs scale
Color: Tan, brownish-grey, and cream
Luster: Dull to waxy

Identified March 29, 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 from silica-rich fluids within sedimentary rock layers, often limestone or chalk. Geological age can range from Precambrian to Holocene.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Currently used as road aggregate, in jewelry as semi-precious gemstones (Jasper), and as a component in flintlock firearms.

Geological facts

Chert was one of the most vital materials for early humans because its conchoidal fracture creates edges sharper than a surgical scalpel. It is chemically very stable and resistant to weathering.

Field identification & locations

Identify in the field by its extreme hardness (will scratch glass/steel), waxy texture when broken, and smoothed, rounded edges if found in gravel pits. Common in limestone outcrops and riverbeds. Collectors look for unique banding or colors.

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