Chert (Jasper/Flint variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, and dark gray; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in sedimentary environments. Its rounded shape suggests it was tumbled in a river or beach environment over thousands of years.

Uses & Applications

Used historically for stone tools and weapons due to its sharp conchoidal fracture. Today used in construction aggregate, road surfacing, and as decorative landscaping stones.

Geological Facts

Chert is so durable that it is often the only rock left remaining after others have weathered away. It is closely related to flint and jasper, differing primarily in color and transparency.

Field Identification & Locations

Identify in the field by its hardness (it can scratch glass and steel), its smooth waxy feel, and its characteristic curved (conchoidal) breaks. This specimen is a common 'river rock' found in gravel pits and along shorelines.

Identified on: 4/27/2026

Mode: Standard