sedimentary

Agate

Chalcedony (SiO2) with impurities

Hardness: 6.5-7 (Mohs); Color: Multi-colored bands, translucent white to orange/red; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline/Trigonal; Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Multi-colored bands, translucent white to orange/red
Luster: Waxy to vitreous

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Multi-colored bands, translucent white to orange/red; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline/Trigonal; Specific Gravity: 2.58-2.64.

Formation & geological history

Formed through the deposition of silica from groundwater into cavities (vesicles) of igneous rocks or sedimentary voids over millions of years.

Uses & applications

Used primarily in jewelry (cabochons, beads), decorative objects, and historically for mortar and pestles due to its hardness and chemical resistance.

Geological facts

Agates are named after the Achates River in Sicily where they were first found. No two agates are perfectly identical due to the unique layering of silica.

Field identification & locations

Can be identified in the field by its translucency (when held to light), waxy feel, and characteristic banding or conchoidal fracture. Often found in riverbeds or lakeside shores like Lake Superior.