sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: White, tan, and dark gray bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: White, tan, and dark gray bands
Luster: Waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: White, tan, and dark gray bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as a chemical precipitate from silica-rich fluids or the accumulation of siliceous organisms (like radiolaria or diatoms) on the seafloor. This process often occurs in deep-marine environments over millions of years.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used today in road construction, as a source for silica, and in jewelry/lapidary as 'flint' or 'jasper'.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture produces edges sharper than a steel razor. Banded chert can sometimes contain microfossils visible under high magnification.

Field identification & locations

Identify in the field by its hardness (it should scratch glass) and its smooth, curved conchoidal fractures. Commonly found in limestone and dolomite formations as nodules or layered beds.