sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray, green-gray, with dark bands; Luster: Waxy to dull; Crystal structure: Cryptocrystalline trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: Gray, green-gray, with dark bands
Luster: Waxy to dull

Identified May 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age can range from Precambrian to Cenozoic.

Uses & applications

Used historically for stone tools and arrowheads; currently used in jewelry (lapidary), as a gemstone, or in construction aggregate and road surfacing.

Geological facts

Banded chert often contains the iron-rich variety known as jasper. Some of the oldest fossils on Earth, found in the Gunflint Chert, are preserved within these types of siliceous rocks.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fracture; commonly found in riverbeds or as nodules within limestone.