Chert / Flint

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Greenish-grey with dark Manganese staining. Luster: Waxy to dull. Crystal 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 by the replacement of limestone. This specimen shows a weathered exterior typical of riverbed or surface exposure.

Uses & Applications

Historically used for making sharp tools and arrowheads. Currently used as road aggregate, in railroad ballast, and occasionally for lapidary work if highly colored.

Geological Facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates edges sharper than a steel scalpel. The dark 'veins' on this specimen are likely manganese oxide stains.

Field Identification & Locations

Identify in the field by checking for conchoidal (shell-like) fractures and its ability to scratch glass. It is commonly found in limestone-rich regions as nodules or bedded layers.

Identified on: 4/27/2026

Mode: Standard