Ivorite, more commonly written ivoirite in the older European literature, is the tektite associated with the Ivory Coast strewnfield in West Africa. Tektites are silica-rich glass bodies formed by the melting and high-velocity ejection of terrestrial target rock during a hypervelocity meteorite impact; they are not themselves of extraterrestrial origin but record the energy of the impact event.

Source crater and age

The Ivory Coast tektites are tied to the Lake Bosumtwi impact structure in Ghana, a roughly 10.5 km diameter crater dated by argon-argon and fission-track methods to approximately 1.07 million years ago, in the Pleistocene. The strewnfield extends across parts of Côte d'Ivoire and Ghana, and microtektite-bearing horizons of the same age have been recovered from deep-sea sediment cores in the equatorial Atlantic, confirming the wider distribution of the ejecta.

Physical and chemical character

Hand specimens are typically small, with most pieces under 5 cm and weights from a few grams to several tens of grams. Colour ranges from black to dark brown in transmitted thin section. The chemistry is broadly andesitic to dacitic, with silica around 67 to 69 weight per cent, and the ivorites are isotopically distinct from the larger Australasian, North American and Central European tektite groups, supporting their assignment to a separate impact event. Refractive index is in the range 1.49 to 1.51 and specific gravity around 2.40, comparable with other tektites.

Use and trade

Ivorites are a collector's material rather than a commercial gem. They are occasionally cabbed or beaded for the natural-history and esoteric markets, but their small average size and the political instability of the source region keep them outside mainstream coloured-stone trade. They are sometimes confused with moldavite by inexperienced buyers; the colour, chemistry and locality readily distinguish the two.