Chert (Jasper/Agate variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Brown, olive green, and white. Luster: Waxy to vitreous. Crystal structure: Hexagonal (microcrystalline). Fracture: Conchoidal (shell-like curves). Specific gravity: 2.58–2.64.

Formation & Geological History

Formed from the accumulation of silica-rich microfossils or via chemical precipitation from silica-rich fluids within other rock types. It is found in geological settings ranging from Precambrian to Cenozoic eras.

Uses & Applications

Historically used for stone tools (arrowheads). Modern uses include landscaping, hardstone carving, and as lapidary material for jewelry or specimen collecting.

Geological Facts

Chert is so hard it can strike sparks against steel. It was the primary material used by prehistoric humans to start fires and craft sharp tools due to its predictable conchoidal fracture pattern.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a steel knife), waxy feel, and sharp, curved edges where broken. Commonly found in stream beds or eroded out of limestone/dolomite formations.

Identified on: 4/24/2026

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