Chert (Jasper/Flint variety)

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, reddish-brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.7.

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical replacement of limestone/dolomite by silica-rich fluids. They are found in rocks of all geological ages from the Precambrian to the present.

Uses & Applications

Historically used for stone tools (arrowheads). Currently used as an ornamental stone, in gemstone tumbling, and as a durable construction aggregate in some regions.

Geological Facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges perfect for cutting tools and weapons. It is often found as nodules or layers within limestone beds.

Field Identification & Locations

Identify in the field by its waxy luster, extreme hardness (it will scratch glass and steel), and curved, shell-like (conchoidal) fractures. Common in riverbeds and limestone outcrops.

Identified on: 4/22/2026

Mode: Standard