mineral

Agate

Silicon Dioxide (SiO2) - variety of Chalcedony

Hardness: 6.5–7 Mohs; Color: Grayish-translucent with inclusions; Luster: Waxy to Vitreous; Crystal Structure: Trigonal (Cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58–2.64

Hardness: 6
Color: Grayish-translucent with inclusions
Luster: Waxy to Vitreous

Identified March 20, 2026More mineral →

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Physical properties

Formation & geological history

Formed in volcanic and metamorphic environments within rock cavities (geodes or vesicles) where silica-rich groundwater deposits layers of minerals over long periods. Can date from the Precambrian to Cenozoic eras.

Uses & applications

Used primarily in lapidary arts for jewelry, beads, and cabochons. Historically used for making mortars and pestles, leather burnishing tools, and decorative carvings due to its hardness.

Geological facts

Agates are often characterized by ribbon-like banding, but in some specimens like the one shown, they appear as translucent chalcedony with moss/plume-like inclusions. It is the official state gemstone of multiple US states, including Oregon and Nebraska.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and lack of visible crystalline grain. In the field, look for riverbeds or volcanic outcrops. To verify, check if it can scratch glass (which it should easily).

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