Irghizite is a variety of tektite, an impact-derived natural glass, formed approximately 900,000 years ago at the Zhamanshin impact crater in north-western Kazakhstan. The material is named after the Irghiz River that runs near the crater, and it represents one of the youngest and best-preserved tektite-forming events known. Irghizite is distinguished from other tektite varieties by its small size, its dark brown to black colour, and its distinctive frothy, twisted and droplet-like surface morphology.

Origin and impact event

The Zhamanshin crater is approximately 14 km in diameter and was identified as an impact structure in the 1970s, with the impact dated to roughly 900,000 years before present. The impact vaporised target rocks of mixed sedimentary and metamorphic composition, and droplets and gobbets of molten glass were ejected from the crater and cooled in flight. Irghizite is the resulting tektite material, found in a strewn field around the crater and in associated impact debris layers. The crater also produced a related impact-glass material called zhamanshinite, distinguished from irghizite by its larger size, lighter colour and more glassy texture.

Physical and chemical properties

Irghizite is an amorphous silica glass with composition reflecting the target rocks at Zhamanshin: high silica content with substantial alumina and minor iron, magnesium, calcium and potassium. The colour ranges from dark brown to nearly black, with the surface often showing a frothy, vesicular texture and twisted, droplet-like shapes that record the cooling of small molten gobbets in flight. Specimen sizes are typically small, in the range of a few millimetres to a few centimetres, with larger pieces uncommon. The hardness is around 6 to 7 on the Mohs scale, comparable to other tektites, with a refractive index near 1.49 to 1.51 depending on composition.

Position among tektite groups

The recognised tektite groups include the Australasian (Australites, Indochinites, Philippinites, etc.), the North American (Bediasites and Georgiaites), the Central European (Moldavites from the Czech Republic and adjacent areas), and the Ivorian (Ivory Coast tektites). Irghizite, with zhamanshinite, sits as a distinct fifth group associated with the Zhamanshin crater, although debate continues about the precise relationship between irghizite and the broader tektite category. Some classifications treat irghizite as a true tektite, others as a related but distinct impact glass.

Trade and collector market

Irghizite is collected and traded primarily as a mineralogical and meteoritical specimen rather than as a faceted or jewellery gem. The small size, dark colour and frothy morphology make it less suited to traditional gem cutting than the moldavite or Australasian tektites. Specimens are sold by dealers specialising in meteorites and impact materials, with prices reflecting size, surface preservation and the relative scarcity of clean, well-formed pieces. Authentication is important: imitations and misidentified specimens occur, and the trade typically requires either dealer reputation or laboratory analysis to confirm Zhamanshin origin.