sedimentary

Chert Nodules in Limestone / Fault Breccia

Silicon Dioxide (SiO2) in Calcium Carbonate (CaCO3) matrix

AI-generated identification · may be incorrect

Hardness: 7 (chert) / 3 (limestone matrix). Color: Dark gray to black angular chert fragments within light tan/beige sandy limestone matrix. Luster: Waxy to dull for chert, earthy for matrix. Fracture: Conchoidal in chert parts.

Hardness: 7 (chert) / 3 (limestone matrix)
Luster: Waxy to dull for chert, earthy for matrix

Identified July 27, 2026More sedimentary →

Explore Chert Nodules in Limestone / Fault Breccia 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 through sedimentary diagenesis where microcrystalline quartz replaces carbonate material, or via tectonic fracturing (faulting) where dark chert is brecciated and cemented by a fine-grained carbonate/silty matrix. Found in sedimentary basins and limestone karst environments worldwide.

Uses & applications

Historically used for knapping stone tools, arrowheads, and striking fire. Today primarily collected as geological specimens or crushed for aggregate and construction material.

Geological facts

Dark chert is often referred to as flint. When subjected to stress, chert fractures with sharp, shell-like (conchoidal) edges, making it ideal for prehistoric toolmakers.

Field identification & locations

Identify in the field by checking hardness: a steel blade will scratch the lighter tan matrix but will not scratch the dark chert core. Commonly found in limestone quarries, riverbeds, and cliff exposures.