mineral

Agate Geode / Nodular Chalcedony

Silicon Dioxide (SiO2) with impurities

Hardness: 6.5-7 (Mohs scale), Color: Variegated grays, browns, and whites; Luster: Waxy to vitreous; Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.58–2.64.

Hardness: 6
Color: Variegated grays, browns, and whites
Luster: Waxy to vitreous

Identified January 25, 2026More mineral →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities of volcanic or sedimentary rocks. Over millions of years, multiple layers of chalcedony crystallize to fill or partially fill the void, creating a geode or nodule.

Uses & applications

Commonly used for lapidary work, jewelry (cabochons), interior decoration when sliced, and as a popular specimen for rock collectors.

Geological facts

The name 'Agate' comes from the Achates River in Sicily, where agates were first discovered in ancient times. Every agate is unique due to the specific mineral impurities present during its slow growth.

Field identification & locations

In the field, look for a 'potato-like' exterior with a rough, pitted texture. It feels heavier than a normal stone of the same size if solid, or lighter if hollow. A common location for such specimens is in basaltic lava flows or dry lake beds in volcanic regions.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral

Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

mineral