Chert (Jasper/Brown Chert)

Physical Properties

Hardness: 7 (Mohs scale); Color: Brown, tan, earthy yellow; Luster: Dull to waxy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & Geological History

Formed as a result of the accumulation of microcrystalline silica, often from the remains of siliceous organisms (like radiolarians or diatoms) or through chemical precipitation in marine or groundwater environments.

Uses & Applications

Historically used for making stone tools due to its sharp edges when fractured. Modern uses include decorative landscaping, flint-knapping enthusiasts, and occasionally as common semi-precious gemstones.

Geological Facts

Chert is extremely durable and chemically stable, often remaining in riverbeds long after softer rocks have eroded away. It is one of the most common materials used by early humans to create arrowheads and scrapers.

Field Identification & Locations

Identify in the field by its hardness (will scratch glass), smooth waxy feel when freshly broken, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and limestone outcrops.

Identified on: 4/17/2026

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