sedimentary

Chert (Jasper variation)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Rusty brown, tan, and gray due to iron impurities; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Rusty brown, tan, and gray due to iron impurities
Luster: Waxy to dull

Identified May 17, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen appears as a secondary replacement in limestone or as a stream-worn pebble.

Uses & applications

Historically used for making stone tools (arrowheads) due to sharp edges; currently used for landscaping, as a gemstone (when polished), and in some construction aggregates.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. The orange-brown hues in this piece are caused by the oxidation of iron minerals, essentially geological rust.

Field identification & locations

Identify in the field by its smooth, waxy feel, sharp edges when broken (conchoidal fracture), and ability to scratch glass. It is commonly found in riverbeds and as nodules within chalk or limestone formations.

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