mineral

Chalcedony (Common Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent white to light grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.58-2.64

Hardness: 6
Color: Translucent white to light grey
Luster: Waxy to vitreous

Identified March 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 from the precipitation of silica-rich groundwater in cavities or veins of igneous and sedimentary rocks. Common in volcanic regions where it fills gas bubbles (vesicles) to form nodules.

Uses & applications

Used primarily in lapidary arts for jewelry, bead making, and carvings. Historically used for making tools and seals. Also used as decorative landscaping stone.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen even under a light microscope. The name likely comes from the ancient Greek town of Chalcedon in Asia Minor.

Field identification & locations

Identify in the field by its waxy luster, translucency, and distinctive conchoidal (shell-like) fracture patterns on broken surfaces. Often found in riverbeds or areas with volcanic history. It will scratch glass but cannot be scratched by a steel knife.