mineral

Agate (chalcedony)

Microcrystalline quartz, SiO₂; likely a gray-brown agate nodule or fragment

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent gray, cream, and brown interior with a waxy to vitreous luster and very fine quartz fibers. It shows conchoidal fracture and no obvious cleavage; specific gravity is about 2.6.

Identified September 5, 2026More mineral →

Explore Agate (chalcedony) 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

Forms when silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in layers over time. Most agates are Cenozoic to older, depending on the host volcanic rocks.

Uses & applications

Used for cabochons, beads, carvings, bookends, and decorative slices; common pieces have modest value, while strongly banded material can be desirable.

Geological facts

The specimen appears partly weathered or broken, exposing a translucent chalcedony core and a rough, lighter outer rind. Color bands may result from iron and other trace impurities.

Field identification & locations

Identify it by its translucency, waxy surface, conchoidal fracture, and hardness sufficient to scratch glass; it is commonly found in volcanic terrains and stream gravels. Confirm with a streak, hardness, and close inspection for true banding.