sedimentary

Agate / Chalcedony Geode Nodule

Silicon Dioxide (SiO2)

Hardness of 7 on the Mohs scale; exhibits brown, tan, and white concentric banding with a crystalline quartz core; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.

Identified August 5, 2026More sedimentary →

Explore Agate / Chalcedony Geode Nodule 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 in gas cavities within volcanic or sedimentary rocks where silica-rich groundwater deposited microscopic quartz crystals in layers over millions of years.

Uses & applications

Used primarily in ornamental lapidary work, making jewelry, decorative slabs, bookends, and sought after by mineral and rock collectors.

Geological facts

Agate banding reflects changes in pressure, temperature, and mineral content of the solutions flowing through the cavity during formation. This specimen shows a classic cavity lined with sparkling quartz crystals surrounded by concentric agate layers.

Field identification & locations

Easily identified by its distinct concentric bands of color and hard quartz center. Commonly found in regions with ancient volcanic activity, such as Brazil, Mexico, Madagascar, and the western United States.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary