sedimentary

Flint with Fossil

Silicon dioxide (SiO2) microcrystalline quartz with fossiliferous inclusions

Hardness: 7 on Mohs scale; Color: Dark grey, brown, or black with a white chalky cortex; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 - 2.65

Hardness: 7 on Mohs scale
Color: Dark grey, brown, or black with a white chalky cortex
Luster: Waxy to vitreous

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments during the Cretaceous period, approximately 65 to 145 million years ago, through the replacement of calcium carbonate in limestone by silica-rich solutions derived from sponge spicules.

Uses & applications

Historically used for stone tools, arrowheads, and fire-starting; currently collected as a geological specimen, used in landscaping, and sometimes for decorative items.

Geological facts

Flint nodules frequently contain well-preserved prehistoric fossils like sponges, sea urchins (echinoids), and brachiopods trapped within the silica matrix during its formation.

Field identification & locations

Easily identified by its dark conchoidal fracture surfaces, white outer cortex, and extreme hardness that can scratch glass. Often found along chalk cliffs, beaches, and glacial drift deposits.

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