sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Tan, beige, brown, and yellowish-grey with layered weathering rind. Luster: Waxy to dull. Fracture: Distinct shell-like (conchoidal) fracture. Structure: Cryptocrystalline.

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified July 24, 2026More sedimentary →

Explore Chert (Flint) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed in marine environments through the chemical precipitation of silica-rich fluids or accumulation of siliceous microscopic organism remains (such as radiolarians and diatoms) within sedimentary beds or limestone nodes.

Uses & applications

Historically used by ancient humans for stone tools, arrowheads, and spark generation. Modern uses include road aggregate, decorative landscaping, and knapping hobbyist specimens.

Geological facts

Chert and flint are essentially the same material, with 'flint' often referring to darker grey or black nodular varieties found in chalk. It breaks with extremely sharp edges, making it the premier tool-making material in prehistory.

Field identification & locations

Identified in the field by its high hardness (scratches glass), smooth waxy feel, sharp edges when broken, and characteristic conchoidal fracturing. Found worldwide in sedimentary rock formations, rivers, and gravel beds.