Chert (containing Iron Oxide spots)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: tan, grey, and yellow-brown; Luster: vitreous to waxy; Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows oxidation (yellow spots), likely from limonite or goethite.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers); currently used in road construction, as decorative stone, or for starting fires (flint equivalent).

Geological Facts

Chert is so hard it can scratch glass and sparks when struck against steel. It was one of the most vital resources for prehistoric humans due to its sharp edges when fractured.

Field Identification & Locations

Identify in the field by its smooth, waxy feel and circular 'conchoidal' fractures. It is commonly found in limestone or chalk beds and along riverbanks.

Identified on: 4/18/2026

Mode: Standard