Chert (Jasper variety)

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, and dark gray/black; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & Geological History

Formed from the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen is water-worn, likely from a river or beach deposit.

Uses & Applications

Used historically for stone tools due to sharp edges when fractured. Modern uses include landscaping, jewelry (lapidary), and as a collecting specimen.

Geological Facts

Chert is so durable that it often survives as pebbles in riverbeds long after the surrounding rock has eroded. Jasper is the opaque variety of chert often colored by iron oxides.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture pattern. Commonly found in gravel pits, riverbanks, and coastal areas.

Identified on: 4/15/2026

Mode: Standard