mineral

Gray Agate

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Smoke gray, tan, translucent brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Smoke gray, tan, translucent brown
Luster: Waxy to vitreous

Identified June 17, 2026More mineral →

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; Color: Smoke gray, tan, translucent brown; Luster: Waxy to vitreous; Crystal Structure: Trigonal/Microcrystalline; Cleavage: None; Specific Gravity: 2.58-2.64.

Formation & geological history

Formed primarily in volcanic and metamorphic rocks through the deposition of silica from groundwater into cavities (vesicles). These processes can span millions of years.

Uses & applications

Used extensively in jewelry (beads, cabochons), ornamental carvings, burnishing tools in leatherwork, and as a collector's gemstone.

Geological facts

Agate is a variety of chalcedony. It was named by Theophrastus, a Greek philosopher, who discovered the stone along the shore of the Achates River in Sicily.

Field identification & locations

Identify by its translucent nature, waxy luster, and conchoidal fracture. Often found in riverbeds or coastal areas where volcanic rock has weathered away. Common in Brazil, India, and the USA.