Chert (Jasper/Chalcedony variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale). Color: Tan, brownish-yellow, and honey tones. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from hydrothermal fluids in sedimentary environments. Common throughout all geological ages from Precambrian to Cenozoic.

Uses & Applications

Used historically for stone tools and arrowheads due to its sharp conchoidal edges. Currently used as an ornamental stone, for lapidary work (polishing and cabochons), and as a landscaping material.

Geological Facts

Chert was one of the first materials used by early humans to create survival tools. Because of its extreme hardness, it can create sparks when struck against steel, similar to flint.

Field Identification & Locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found in stream beds or as nodules in limestone. Collectors should look for unique banding or color patterns.

Identified on: 4/19/2026

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