mineral

Agate

Silicon Dioxide (SiO2) - Banded Chalcedony

Hardness: 6.5-7 on Mohs scale; Color: Multi-colored bands (white, grey, brown, red); Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.

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

Identified January 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed primarily within volcanic and metamorphic rocks. It develops as silica-rich groundwater fills cavities (vesicles) in lava flows, depositing layers of microcrystalline quartz over long periods. Most specimens date from the Cenozoic to the Precambrian eras.

Uses & applications

Used extensively in jewelry as gemstones (cabochons, beads), decorative carvings, and paperweights. Due to its hardness and resistance to acids, it is also used industrially to make mortars and pestles for laboratory chemicals.

Geological facts

Agate is named after the Achates River in Sicily where it was first discovered. Every agate is unique; the banding patterns reflect the changing chemistry of the fluids that entered the cavity during its formation.

Field identification & locations

Identify in the field by its distinct concentric banding, waxy texture on broken surfaces, and translucency when held to light. Common locations include Brazil, Uruguay, and the Lake Superior region of the United States. It is a favorite for rockhounds because of its durability and beauty when polished.