Chert (or Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, tan, and brown with waxy luster; Crystal Structure: Microcrystalline; Cleavage: None (distinct conchoidal fracture); Specific Gravity: 2.5-2.8

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments; this specific piece appears to have undergone significant water-tumbling and erosion, likely in a river or coastal setting.

Uses & Applications

Historically used for stone tools and fire-starting; currently used for decorative stone, gravel, and as a collector's specimen for studying geological textures.

Geological Facts

Chert is so durable that it often survives long after the surrounding rock has weathered away. It was one of the most important minerals for ancient humans due to its ability to hold a sharp edge when fractured.

Field Identification & Locations

Identify in the field by its waxy luster and smooth, curved (conchoidal) breaks. It is very hard and will scratch glass. Look for it in limestone formations or as river pebbles.

Identified on: 4/15/2026

Mode: Standard