sedimentary

Chert (River Stone/Pebble)

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, or olive-drab; Luster: Waxy to dull; Crystal structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Tan, beige, or olive-drab
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or olive-drab; Luster: Waxy to dull; Crystal structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation in saltwater environments. This specimen appears water-worn, indicating it was shaped by fluvial (river) or coastal erosion during the Holocene or Pleistocene.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges when broken. Today used as construction aggregate, road base, and common decorative landscaping stone.

Geological facts

Chert is so durable that it often remains as pebbles in riverbeds long after the surrounding limestone or shale has eroded away. It is chemically identical to flint, but 'chert' is the preferred geological term for lighter-colored specimens.

Field identification & locations

Identify in the field by its smooth, waxy texture and its ability to scratch glass. It will not react with acid (unlike limestone). Commonly found in gravel bars, riverbanks, and glacial till.