Chert (Flint variety)

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or gray; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or by chemical precipitation in limestone or chalk beds. Commonly found in Paleozoic to Mesozoic sedimentary layers.

Uses & Applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as a semi-precious stone in jewelry making.

Geological Facts

Chert was one of the most important minerals for early humans because of its ability to break into extremely sharp edges. This specific specimen shows distinct conchoidal fracturing ripples.

Field Identification & Locations

Identify in the field by its smooth, waxy surface and characteristic curved (conchoidal) breaks. It can scratch glass and will not react with acid like the limestone it often sits in.

Identified on: 5/15/2026

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