sedimentary

Chert (Smooth River Pebble)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, brown; Luster: Waxy to dull; Structure: Cryptocrystalline (grains too small to see with a microscope); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Tan, beige, brown
Luster: Waxy to dull

Identified June 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen is a water-worn, smoothed pebble likely shaped over thousands of years in a riverbed.

Uses & applications

Historically used for making stone tools (flintknapping). Today used as decorative gravel, in landscaping, as a gemstone (jaspers), and as an abrasive.

Geological facts

Chert is so hard it can create sparks when struck against steel. It is chemically identical to quartz but has a different internal structure. Ancient people valued it for its predictable, razor-sharp fracture edges.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy texture, and its smooth, rounded shape if found near water. Common in limestone deposits and riverbeds worldwide.