Banded Flint (Chert)

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and gray bands; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed as nodules in sedimentary rocks like chalk or limestone through the replacement of calcium carbonate by silica-rich groundwater. The bands represent different stages of mineral deposition.

Uses & Applications

Historically used for stone tools and fire-starting (flintknapping); currently used for architectural decoration, jewelry (cabochons), and as a gravel material.

Geological Facts

Banded flint is a common variety of chert. The distinctive stripes are often the result of rhythmic precipitation of silica or varying impurities during the lithification process.

Field Identification & Locations

Identify by its characteristic waxy surface, conchoidal (shell-like) fracture patterns, and parallel banding. Commonly found in coastal chalk cliffs and riverbeds.

Identified on: 5/4/2026

Mode: Standard