Chert (Jasper-bearing)

Physical Properties

Hardness: 7 (Mohs scale); Color: Rusty orange/brown exterior (limonite/hematite staining), greenish-grey fresh break; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed by the precipitation of silica from seawater or groundwater, often replacing organic material or occupying voids in carbonate rocks. This specimen shows heavy weathering and oxidation in a soil-rich environment.

Uses & Applications

Historical use for stone tools (arrowheads/scrapers), modern use in construction aggregate, and lower grades used in decorative landscaping.

Geological Facts

Chert was one of the most important minerals for early humans due to its ability to be knapped into extremely sharp edges. The reddish-orange coating is a result of iron leaching from the surrounding soil, a common feature in lateritic or clay-rich regions.

Field Identification & Locations

Identify in the field by its distinct conchoidal (shell-like) fracture, high hardness (will scratch glass), and smooth, waxy texture on unweathered surfaces. Commonly found in stream beds or limestone outcrops.

Identified on: 4/19/2026

Mode: Standard