mineral

Agate

Silicon dioxide (SiO2)

Hardness: 6.5-7 (Mohs); Color: Multi-colored bands (yellow, brown, white, tan); Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: Multi-colored bands (yellow, brown, white, tan)
Luster: Waxy to vitreous

Identified June 17, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Multi-colored bands (yellow, brown, white, tan); Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal); Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed in cavities (vesicles) of volcanic rocks or ancient sedimentary rocks. Silica-rich groundwater precipitates layers of microscopic quartz crystals over long periods, often in Cenozoic or Mesozoic age formations.

Uses & applications

Used primarily in lapidary arts, jewelry, ornaments, and as a decorative collector's specimen. Historically used for making mortar and pestles due to hardness.

Geological facts

Agate is a variety of chalcedony. Each agate is unique due to the distinct banding patterns formed by varying mineral impurities during the deposition process. It is often the state rock or gemstone for several US states, including Oregon and Montana.

Field identification & locations

Identify by looking for translucent edges, waxy luster, and distinct concentric or moss-like banding. Commonly found in riverbeds, lake shores (like Lake Superior), and volcanic gravel deposits.