sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Brown, tan, cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 Mohs scale
Color: Brown, tan, cream
Luster: Waxy to dull

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Brown, tan, cream; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from seawater or by the accumulation of siliceous remains of microorganisms like radiolarians or diatoms. The banding represents changes in sediment and mineral deposition over time.

Uses & applications

Historically used for stone tools and arrowheads; currently used as decorative gravel, in lapidary work for cabochons, and as a collector's specimen.

Geological facts

Chert has a conchoidal fracture, allowing it to be knapped into sharp edges. It was one of the most important minerals for early human survival for weaponry and fire-starting.

Field identification & locations

Identify by its waxy appearance, extreme hardness (it will scratch glass), and smooth, shell-like fracture surfaces. Frequently found in limestone and dolomite beds worldwide.