sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, and gray bands; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brown, tan, and gray bands
Luster: Waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and gray bands; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater in sedimentary basins and marine environments.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Modern uses include lapidary work, jewelry (cabochons), and as a decorative landscaping stone.

Geological facts

Chert was one of the first minerals utilized by prehistoric humans. The banding represents changes in the depositional environment or mineral impurities like iron oxide over time.

Field identification & locations

Identify by its hardness (scratches glass), waxy texture when broken, and smooth river-worn appearance. Commonly found in riverbeds, glacial tills, and within limestone formations.