Chert (Jasper)

Physical Properties

Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Dull to waxy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed by the accumulation of silica-rich organic remains or chemical precipitation from hydrothermal fluids in sedimentary environments. Common in marine deposits where silica replaces carbonate material.

Uses & Applications

Historically used for stone tools (arrowheads). Modern uses include gemstones, landscaping, and as a component in construction aggregates. High-quality specimens are used for lapidary work.

Geological Facts

The red color in this specimen is likely due to iron oxide (hematite) inclusions. Chert is so hard it can scratch glass and produce sparks when struck against steel.

Field Identification & Locations

Identify in the field by its characteristic conchoidal (shell-like) fracture, extreme hardness, and waxy texture on fresh surfaces. Commonly found in riverbeds, desert pavements, and limestone outcrops.

Identified on: 5/3/2026

Mode: Standard