sedimentary

Chert (with Calcite layering)

Silicon Dioxide (SiO2) with Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 7 (chert) / 3 (calcite); Color: Dark gray/brown matrix with cream-white layering; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture on chert).

Hardness: 7 (chert) / 3 (calcite)
Color: Dark gray/brown matrix with cream-white layering
Luster: Dull to waxy

Identified July 10, 2026More sedimentary →

Explore Chert (with Calcite layering) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (chert) / 3 (calcite); Color: Dark gray/brown matrix with cream-white layering; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture on chert).

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments; the layering indicates subsequent mineralization by carbonate fluids (calcite) within a sedimentary nodule or bed.

Uses & applications

Historically used for stone tools (flint knapping); currently used as construction aggregate or collected as mineral specimens.

Geological facts

Chert is extremely durable and chemically stable, often preserving fine details of ancient environments. Layers like the one pictured often represent a change in the chemical environment during the rock's formation or diagenesis.

Field identification & locations

Identify in the field by its waxy texture and inability to be scratched by steel; the white layer may fizz if exposed to weak acid (HCl). Found globally in sedimentary basins.