sedimentary

Chalcedony (Chert/Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: tan to honey brown, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.65

Hardness: 6

Identified July 10, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: tan to honey brown, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.6-2.65

Formation & geological history

Formed through the accumulation of silica-rich fluids in limestone or chalk beds, or as a replacement mineral in organic matter. Frequently found in sedimentary environments where it precipitates from groundwater.

Uses & applications

Abrasives, jewelry (when high quality), historical tool-making (stone age tools), and as a collector specimen.

Geological facts

This material is often called 'flint' when found in chalk and 'chert' in other sedimentary rocks. It was the primary material used by prehistoric humans to create sharp cutting tools due to its conchoidal fracture which produces razor-sharp edges.

Field identification & locations

Identify in the field by its waxy luster, smoothness, and the distinctive curved 'shell-like' fracture patterns when broken. Common in gravel beds and limestone outcrops.