Chert (Jasper/Flint Pebble)

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, beige, and reddish-brown mottling; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. Often found as nodules in limestone or as water-worn pebbles in riverbeds.

Uses & Applications

Historically used for stone tools and fire-starting. Currently used in road construction, as tumbled decorative stones, and occasionally in lapidary work for jewelry.

Geological Facts

Chert is so durable that it often survives long after the surrounding rock has eroded away, which is why it is commonly found as smooth pebbles in gravel or on beaches.

Field Identification & Locations

Identify in the field by its high hardness (it will scratch glass) and its smooth, rounded 'river rock' texture. Look for the characteristic shell-like (conchoidal) curves if the rock is chipped.

Identified on: 4/24/2026

Mode: Standard