Chert (Jasper variation)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Forms from the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Can be found in various geological ages from Precambrian to Cenozoic.

Uses & Applications

Primarily used for lapidary work, jewelry (cabochons), and historically for tool-making (arrowheads) due to its sharp edges when fractured.

Geological Facts

Chert is one of the most durable sedimentary rocks. Red variations are often called Jasper and owe their color to iron oxide inclusions.

Field Identification & Locations

Identify in the field by its smooth, waxy feel, hardness (it can scratch glass), and conchoidal fracture patterns. Commonly found in river beds, gravel pits, and limestone outcrops.

Identified on: 5/3/2026

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