sedimentary

Flint

Chert (Cryptocrystalline Quartz, SiO2)

Hardness: 7 (Mohs scale); Color: Brownish-orange exterior (iron-stained cortex) with grey internal glassy core; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Luster: Waxy to vitreous

Identified July 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Upper Cretaceous period (approx. 66-100 million years ago) through the accumulation of silica-rich organic remains (like sea sponges) within chalk layers. This specific specimen shows heavy iron staining and water-rolling typical of Pleistocene glacial deposits.

Uses & applications

Historically used for stone tools (knapping) and sparking fires. Modernly used as high-quality aggregate in construction, road surfacing, and decorative landscaping. High-quality specimens are used in jewelry and lapidary art.

Geological facts

Flint was the primary 'high-tech' material of the Stone Age due to its ability to produce razor-sharp edges. The location (Essex/Suffolk coast, UK) is world-famous for its 'Cretaceous Chalk' flint deposits.

Field identification & locations

Identified by its conchoidal (shell-like) fracture, its ability to scratch glass, and the presence of a weathered white or orange 'cortex' (skin) covering a dark, glassy interior. Common on beaches and in gravel pits throughout Southern and Eastern England.