sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Banded green, black, and grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Banded green, black, and grey
Luster: Waxy to vitreous

Identified May 29, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Banded green, black, and grey; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed primarily through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation on the ocean floor, often during the Precambrian or Paleozoic eras. The banding represents changes in mineral impurities during deposition.

Uses & applications

Used historically for stone tools and arrowheads due to its sharp fracture edges. Today it is used as decorative stone, in lapidary work for cabochons, and as drainage or construction aggregate.

Geological facts

Chert was one of the first materials utilized by early humans for tool-making. Famous varieties include Flint and Jasper. Banded versions are often called 'ribbon chert' or 'striped chert'.

Field identification & locations

Identified in the field by its extreme hardness (scratches glass), smooth waxy feel, and distinctive shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or coastal deposits.