Agate

Physical Properties

Hardness: 6.5-7 Mohs; Color: Varied, translucent grey with brown inclusions; Luster: Vitreous to waxy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.

Formation & Geological History

Formed through the deposition of silica from groundwater in the cavities of igneous rocks, primarily volcanic lava. Some can be hundreds of millions of years old, often found in ancient volcanic flows.

Uses & Applications

Used primarily in jewelry as cabochons, decorative carvings, burnishing tools, and as a collector's specimen.

Geological Facts

The name Agate comes from the Achates River in Sicily, now known as the Dirillo River, where the stones were first found in ancient times. It is a variety of chalcedony characterized by its fineness of grain and brightness of color.

Field Identification & Locations

Identify by its waxy luster, translucency when held to light, and circular or banded growth patterns. Commonly found in riverbeds or near volcanic fields.

Identified on: 5/2/2026

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