mineral

Agate (Carnelian / Chalcedony)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, translucent grey/white; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Fracture: Conchoidal.

Hardness: 6
Color: Reddish-brown, translucent grey/white
Luster: Waxy to vitreous

Identified April 4, 2026More mineral →

Explore Agate (Carnelian / Chalcedony) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Reddish-brown, translucent grey/white; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Fracture: Conchoidal.

Formation & geological history

Formed as a secondary mineral in volcanic rock cavities (vugs) or sedimentary veins through the deposition of silica from groundwater. The red coloration is typically caused by iron oxide (hematite) inclusions.

Uses & applications

Used in gemstone jewelry, semi-precious carvings, ornamental stones, and historically for making burnishing tools or industrial mortars and pestles.

Geological facts

Agate is a variety of chalcedony. The reddish variety is specifically known as Carnelian. It has been used as a gemstone for over 4,500 years, notably by the ancient Egyptians and Sumerians for signet rings and amulets.

Field identification & locations

Identify in the field by its waxy luster when broken, translucent edges when held to light, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or areas with weathered volcanic soil.