Kuruman is a town and the surrounding administrative district in the John Taolo Gaetsewe District Municipality of the Northern Cape Province of South Africa. The district is internationally significant as the principal source of tiger's eye and the related materials hawk's eye and pietersite-type chatoyant chalcedonies, all of which originate in the banded ironstone formations of the Asbestos Mountains and the Kuruman Hills.

Geology

The Kuruman district lies within the Griqualand West Basin of the Transvaal Supergroup, a Palaeoproterozoic sequence approximately 2.4 to 2.2 billion years old. The crocidolite (a fibrous blue amphibole, the asbestiform variety of riebeckite) occurs in cross-fibre veins within the Kuruman Iron Formation. Where the original crocidolite has been pseudomorphously replaced by silica with retention of the fibrous structure, the result is tiger's eye (gold to brown) or hawk's eye (blue, the original unaltered crocidolite colour preserved in the silicified fibre). The chatoyant or cat's-eye effect arises from the parallel orientation of the original fibres now preserved in chalcedony.

Production history

Tiger's eye was first commercially extracted from the Kuruman district in the late nineteenth century, and the area has been the principal world source for the material throughout the twentieth century. Production peaked in the mid-twentieth century alongside the larger crocidolite asbestos mining industry of the Northern Cape. The asbestos industry was subsequently shut down on health grounds (the Cape Asbestos cases and South African asbestos legislation), and tiger's eye production now operates on a smaller artisanal scale from former asbestos workings, with the silicified material extracted but the fibrous unaltered crocidolite handled under controlled conditions.

South Africa remains the dominant source, with smaller production in Western Australia (Hamersley Range), Namibia, India and the United States.

Material varieties

The principal Kuruman materials are tiger's eye proper (gold to red-brown, the silica-replaced form), hawk's eye (slate-blue to greenish-blue, retaining unaltered crocidolite), and various banded and brecciated combinations. Heat-treated tiger's eye produces the deep red red tiger's eye; the colour change is from the oxidation of iron compounds and is generally considered stable. Tumbled and beaded tiger's eye remains a major item of South African gemstone export.

Trade

Most Kuruman material reaches the international market through Cape Town and Johannesburg dealers, with substantial volumes also moving directly to lapidary buyers from China and India. Pricing is modest by international standards; the material is high-volume rather than high-value, with most sales by the kilogramme rather than by individual stone. Specimen-grade pieces with strong chatoyancy and clean banding command premiums.