Chert (specifically Jasper/Flint pebble)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Opaque tan, brown, and ochre. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary beds. This specimen is water-worn and likely from the Cenozoic era based on typical surface deposits.

Uses & Applications

Historically used for stone tools and starting fires (striking against steel). Modernly used in landscaping, as tumbling rough for hobbyists, and in jewelry (as Jasper).

Geological Facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges for arrowheads and scrapers. Different colors are caused by trace inclusions of iron oxides.

Field Identification & Locations

Identify in the field by its extreme hardness (will scratch glass) and waxy, smooth texture compared to other river rocks. Commonly found in riverbeds, gravel pits, and limestone formations.

Identified on: 4/19/2026

Mode: Standard