sedimentary

Chert Concretion / Nodule

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, yellowish-brown; Luster: Waxy to dull; Texture: Cryptocrystalline, smooth conchoidal fracture; Cleavage: None

Hardness: 6
Color: Tan, beige, yellowish-brown
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, yellowish-brown; Luster: Waxy to dull; Texture: Cryptocrystalline, smooth conchoidal fracture; Cleavage: None

Formation & geological history

Formed by the chemical precipitation of silica within sedimentary rock layers, often limestone or chalk. Many originate from the accumulation of silica-rich organic remains like sponges or diatoms. Age varies significantly by deposit floor.

Uses & applications

Historically used for making stone tools (arrowheads/scrapers) due to conchoidal fracture. Currently used in road construction, landscaping, and as a collector specimen.

Geological facts

Chert nodules are often mistaken for fossils because of their rounded, organic shapes. In some regions, they are referred to as 'flint' if found in chalk.

Field identification & locations

Identify in the field by its hardness (will scratch steel) and its smooth, shell-like fracture pattern when broken. Commonly found in riverbeds or eroding out of limestone cliffs.