Chert (Jasper/Flint variant)

Physical Properties

Hardness: 7 (Mohs scale); Color: Brownish-tan; Luster: Waxy to sub-vitreous; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific Gravity: 2.65.

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids in sedimentary basins. Often found in nodules or bedded layers.

Uses & Applications

Historically used for stone tools/weapons (knapping) due to its sharp edges. Currently used as an abrasive, in landscaping, and as a semi-precious gemstone in jewelry.

Geological Facts

Chert is so hard it can strike sparks against steel. It has been used by humans for over 2 million years to create tools like arrowheads and scrapers.

Field Identification & Locations

Identify in the field by its waxy texture, smooth 'shell-like' (conchoidal) fractures, and its ability to scratch glass easily. Commonly found in limestone or chalk deposits.

Identified on: 4/17/2026

Mode: Standard