sedimentary

Chert with Limestone matrix

Microcrystalline silica (SiO2) in Calcite (CaCO3) matrix

AI-generated identification · may be incorrect

Hardness: 7 for chert, 3 for limestone; Color: Gray, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in chert)

Hardness: 7 for chert, 3 for limestone
Color: Gray, tan, and creamy white
Luster: Waxy to dull

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 for chert, 3 for limestone; Color: Gray, tan, and creamy white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture in chert)

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within marine limestone beds. Common in many geological periods where marine environments existed.

Uses & applications

Historically used for making stone tools; currently used as aggregate, decorative stone, and by rockhounds for lapidary work.

Geological facts

The chert part of this specimen is significantly harder than the surrounding limestone and will scratch glass. Chert nodules often preserve microfossils.

Field identification & locations

Identified by its waxy luster and distinctive conchoidal (shell-like) fracture patterns on broken gray surfaces. Commonly found in limestone outcrops, riverbeds, and gravel pits.