sedimentary

Chert (Chalcedony/Agate)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brownish-yellow, tan, and translucent white; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65

Hardness: 6
Color: Brownish-yellow, tan, and translucent white
Luster: Waxy to vitreous

Identified May 3, 2026More sedimentary →

Explore Chert (Chalcedony/Agate) 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 via the precipitation of silica from groundwater or within sedimentary rock layers like limestone. This specimen appears water-worn, likely tumbled in a river or coastal environment over thousands of years.

Uses & applications

Historically used for making stone tools; currently used for decorative stone, lapidary work, jewelry (when polished), and aggregate in construction.

Geological facts

This specific sample shows clear waxy luster and translucency typical of chalcedony. Chert is so durable that it often survives long after the surrounding rock has eroded away.

Field identification & locations

Identified by its waxy texture, lack of visible crystals, and conchoidal (shell-like) fracture patterns. Found globally in gravel beds, beaches, and sedimentary basins.