sedimentary

Chert (Brown variety / Common Jasper)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Brown, tan, or earthy yellow; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, or earthy yellow
Luster: Waxy to dull

Identified February 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. These specimens often originate in limestone or chalk beds as nodules and can range from ancient Precambrian to recent geological ages.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modern uses include landscaping, road aggregate, jewelry (when polished as jasper), and as a gemstone for lapidary hobbyists.

Geological facts

Because it is extremely hard and chemically stable, chert often survives erosion that destroys surrounding rock. It was one of the most important minerals for early humans to create survival tools like arrowheads and scrapers.

Field identification & locations

Identify in the field by its smooth, waxy surface and its ability to scratch glass. Look for curved, shell-like (conchoidal) fractures on broken edges. It is commonly found in riverbeds or within sedimentary rock outcrops globally.