Chert (Beach Pebble)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Greyish-white with iron staining; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen was likely shaped and smoothed by wave action in a river or coastal environment.

Uses & Applications

Used historically for stone tools (flintknapping); currently used in construction aggregate, road surfacing, and as decorative landscape gravel.

Geological Facts

Chert is so hard it can scratch steel. This specific specimen shows 'pitting' which occurs when softer inclusions weather out of the silica matrix over time.

Field Identification & Locations

Identify in the field by its hardness and smooth, waxy feel. It will not react with acid (unlike limestone) and often has rounded edges from water erosion. Common in sedimentary basins worldwide.

Identified on: 4/26/2026

Mode: Standard