Chert (Jasper nodule)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, yellowish-brown, ochre; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the precipitation of silica from seawater or groundwater, often replacing organic material or filling cavities in limestone or shale. This specimen shows significant rounding from water transport in a river or stream environment.

Uses & Applications

Historically used for making stone tools (flintknapping); current uses include lapidary work, jewelry (especially when patterned as Jasper), and as a decorative landscaping stone.

Geological Facts

Chert is so chemically stable and hard that it can survive for millions of years in riverbeds. The brown coloration in this specific nodule is likely due to the inclusion of iron oxides like goethite or limonite.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth texture. Look for conchoidal (shell-like) fractures where bits have chipped off. Often found in gravel bars of ancient or modern river systems.

Identified on: 4/30/2026

Mode: Standard