Banded Chert (River Stone)

Physical Properties

Hardness: 6.5-7.0 (Mohs scale), Color: layers of grey, tan, and brown, Luster: waxy to vitreous when polished, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture).

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments; this specific specimen has been water-worn and polished in a river or beach setting.

Uses & Applications

Historically used for stone tools and fire-starting; modern use includes rock tumbling, lapidary art, and decorative landscaping.

Geological Facts

Chert is chemically identical to quartz but has a microcrystalline structure. Its sharp conchoidal fracture made it the primary material for arrowheads and scrapers for indigenous peoples globally.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, rounded river-worn shape. Commonly found in riverbeds and gravel pits.

Identified on: 5/20/2026

Mode: Standard