Chert (Jasper/Flint variety)

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and reddish-grey; Luster: Dull to waxy; Structure: Microcrystalline; Fracture: Conchoidal; Cleavage: None.

Formation & Geological History

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. Most common in Paleozoic and Mesozoic strata.

Uses & Applications

Historically used for stone tools and weapons (arrowheads) due to its sharp edges when fractured. Currently used in road construction, as decorative landscaping stone, and occasionally in lapidary work.

Geological Facts

Chert is so hard it can scratch steel and produce sparks when struck against iron, which is why flint (a variety of chert) was essential for early firearms and fire-starting.

Field Identification & Locations

Identify by its extreme hardness, waxy texture on fresh breaks, and curved (conchoidal) fracture patterns. Frequently found as nodules in limestone or chalk beds.

Identified on: 5/3/2026

Mode: Standard