sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: ranges from white to gray, brown, black, or reddish-brown. Luster: waxy to vitreous. Crystal structure: microcrystalline/cryptocrystalline (quartz). Fracture: conchoidal. Specific gravity: 2.60 - 2.65.

Hardness: 7 on the Mohs scale
Color: ranges from white to gray, brown, black, or reddish-brown
Luster: waxy to vitreous

Identified July 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via the chemical or biochemical precipitation of silica from aqueous solutions, often replacing limestone or accumulating from the skeletal remains of siliceous organisms like radiolaria and diatoms during the Mesozoic and Paleozoic eras.

Uses & applications

Historically used by early humans for making stone tools (arrowheads, scrapers, blades) due to its sharp conchoidal fracture. Also used in abrasives, road aggregate, and historically for striking fire.

Geological facts

Chert includes well-known varieties such as flint and jasper. Because of its durability and conchoidal fracture, it was one of the most important materials in human stone-age technology.

Field identification & locations

Can be identified in the field by its distinct waxy luster, hardness (scratches glass), and sharp conchoidal fracture edges. Found worldwide in sedimentary sequences, particularly within chalk or limestone formations.