sedimentary

Chert or flint

Microcrystalline quartz (SiO₂), often chalcedony

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; brown to gray, waxy or dull luster, opaque to translucent edges, and conchoidal fracture without cleavage. The specimen appears weathered and iron-stained, with possible lighter chalcedonic patches.

Identified September 4, 2026More sedimentary →

Explore Chert or 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

Forms when silica-rich groundwater replaces or fills cavities in limestone, chalk, or volcanic sediments; many examples are Paleozoic to Cenozoic in age. It commonly occurs as nodules, beds, or fragments in sedimentary rocks.

Uses & applications

Used historically for sharp tools and fire-starting, and today for lapidary work, carvings, aggregate, and educational collections; attractive varieties may be polished as ornaments.

Geological facts

Freshly broken chert produces very sharp conchoidal edges and may give sparks against steel, though this should be tested cautiously. Flint is a dark, compact variety of chert, while jasper is an opaque, often more vividly colored silica-rich variety.

Field identification & locations

Identify it by its glassy/conchoidal fracture, absence of visible grains, high hardness, and inability to scratch with a steel knife; common sources include limestone regions worldwide. The image alone cannot distinguish chert confidently from weathered jasper or quartz-rich rock.