sedimentary

Chert (Agate / Jasper pebble)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on the Mohs scale. Color: Brownish-grey to yellowish-tan with subtle banding or translucency. Luster: Waxy to vitreous when wet or polished. Structure: Microcrystalline/Cryptocrystalline. Specific Gravity: ~2.65.

Hardness: 6
Luster: Waxy to vitreous when wet or polished

Identified July 27, 2026More sedimentary →

Explore Chert (Agate / Jasper pebble) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed via the accumulation of silica-rich biogenic ooze or chemical precipitation of silica in groundwater and marine environments. Often smoothed and rounded by river, lake, or glacial water erosion over millions of years.

Uses & applications

Commonly collected as tumbled stones, polished river pebbles, lapidary material, or used historically for stone tools due to its conchoidal fracture.

Geological facts

Chert and jasper have been utilized by humans for over a million years to create sharp-edged tools, arrowheads, and fire-starting flints due to their hardness and predictable fracture patterns.

Field identification & locations

Identify by its hardness (scratches glass), smooth waxy feel, conchoidal fracture, and lack of visible mineral grains. Widespread in riverbeds, lake shores, and glacial deposits globally.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)

sedimentary

Shale

Shale (clastic sedimentary rock)

sedimentary