sedimentary

Chert with Fossil inclusions

Microcrystalline Quartz (SiO2) with biogenic inclusions

AI-generated identification · may be incorrect

Hardness: 7 Mohs; Color: Gray, tan, and cream; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.

Hardness: 7 Mohs
Color: Gray, tan, and cream
Luster: Dull to waxy

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Gray, tan, and cream; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Opaque.

Formation & geological history

Formed in marine environments through the precipitation of silica or the accumulation of siliceous skeletal remains (like diatoms or radiolarians). Significant fossilization often occurs in the Paleozoic and Mesozoic eras.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers); currently used for road aggregate and as a collector's specimen if fossiliferous.

Geological facts

Chert is so durable that it often survives intense weathering that destroys surrounding limestone or chalk. It was one of the first materials used by early humans for fire-starting and weaponry.

Field identification & locations

Identify by its hardness (scratches glass), smooth waxy feel, and conchoidal (shell-like) fractures. Commonly found as nodules in limestone beds or as rounded pebbles in riverbeds and beaches.