Irgizite

Irgizites are rare impact glasses from Kazakhstan, associated with the Zhamanshin impact structure. They formed approximately 900,000 years ago when a cosmic body struck the Earth and the energy of the impact melted part of the rocks at the surface. The resulting melt was ejected into the surrounding area and solidified into natural glass during rapid cooling.

Irgizites belong to a group of tektite-like impact glasses. They often occur as small droplet-shaped, elongated or irregular forms, and some specimens show evidence of shaping during the flight of molten material. They are typically dark brown to almost black and have a glassy character.

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Zhamanshin Impact Crater

The Zhamanshin impact structure is located in Kazakhstan, approximately 200 km north of the Aral Sea. The crater is approximately 14 km in diameter and its age is estimated at around 900,000 years.

Several types of natural glass were formed during the impact. In addition to irgizites, the area also contains zhamanshinites, which differ from irgizites in their chemical composition, structure and mode of formation.

Appearance and Composition of Irgizites

Irgizites are silica-rich glasses. Analysed specimens contain approximately 69–76% SiO₂. They often consist of a homogeneous dark brown glassy mass with numerous bubbles and may occur as droplets, curved rods, filaments or other irregular splash-form shapes.

Chemical analyses have also revealed an admixture of material from the cosmic body that caused the impact. Elevated concentrations of certain elements, particularly nickel and cobalt, indicate that part of the impactor material mixed with the molten terrestrial rocks during the formation of the glass.

Irgizites and Tektites

Irgizites resemble tektites in their appearance and some of their shapes, but scientifically they are directly associated with the Zhamanshin crater and are classified as impact glasses. Unlike classical tektites, they were not transported hundreds or thousands of kilometres from their place of origin, but represent material ejected in connection with a specific impact structure.