mineral

Chalcedony (Botryoidal or Agate nodule)

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Translucent tan, honey-yellow, or greyish; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None; Specific gravity: 2.58–2.64.

Hardness: 6
Color: Translucent tan, honey-yellow, or greyish
Luster: Waxy to vitreous

Identified March 9, 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-rich water in cavities (vugs) within volcanic ash or basaltic rock. It precipitates at relatively low temperatures, often resulting in smooth, rounded, or 'bumpy' (botryoidal) surfaces. These specimens can range in age from the Cenozoic to much older depending on the host formation.

Uses & applications

Commonly used in lapidary work for cabochons, beads, and carvings. High-quality specimens are popular for rock collecting. Historically used for making tools and seals due to its toughness and lack of cleavage.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. It often forms the base material for named varieties like agate, carnelian, and onyx.

Field identification & locations

Identify in the field by its waxy luster, translucency, and conchoidal (shell-like) fracture when broken. It cannot be scratched by a steel knife. Frequently found in desert regions, gravel beds, or weathering out of volcanic rock. Common locations include the Western USA, Brazil, and India.

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