Khorasan, in north-eastern Iran, is one of the most historically significant gem-producing regions in the world, principally for turquoise from the deposits at Neyshabur, also rendered Nishapur. The region has supplied turquoise continuously for at least two thousand years and arguably much longer, making the Neyshabur mines among the oldest continuously worked gem mines anywhere.

Geological setting

The Neyshabur turquoise deposits lie in the Binalud Mountains north of the city of Neyshabur in modern Razavi Khorasan Province. The turquoise occurs in a hydrothermally altered trachyte and trachyandesite host rock, with mineralisation along veins and as pocket fillings. The colour-causing element is copper, with traces of iron and other elements influencing the saturation and hue. The classic Neyshabur material is a robin's-egg blue with little or no matrix, although a wide range of hues and matrix types occurs.

Historical importance

The Neyshabur mines supplied turquoise to the courts of the Achaemenid, Sasanian, Islamic, Safavid, and Qajar empires, with the gem appearing in jewellery, sword fittings, miniatures, and religious objects. Persian turquoise was widely traded along the Silk Road and is found in archaeological contexts from China to the Mediterranean. The literature in Persian, Arabic, and later European sources is extensive; works on gems by al-Biruni in the eleventh century and later treatises document the prestige of Khorasan turquoise.

Quality grading

The trade has long recognised an internal hierarchy among Khorasan turquoise. The highest grade is the so-called angushtarie or ring-stone grade, intensely blue, free of matrix, and suitable for cabochon work in the finest jewellery. Lower grades include matrix-bearing material with brown or black veins, paler stones, and stones with greenish casts that the trade regards as less desirable. Persian dealers maintain detailed grading vocabularies that have been borrowed by Western references.

Treatment and stabilisation

Turquoise is porous and many stones are stabilised with resin or wax to enhance colour stability and durability. Untreated Khorasan turquoise of high grade commands a substantial premium over treated material, although treatment is widespread and considered acceptable provided it is disclosed. The major laboratories including GIA and Gem Research Swisslab provide treatment-detection reports for high-value turquoise.

Modern production

Production at Neyshabur continues, although on a smaller scale than in earlier centuries, with output dispersed among small-scale operations under regional Iranian regulatory oversight. International trade in Iranian turquoise has been complicated since the 1980s by sanctions and trade restrictions, and significant quantities of Khorasan turquoise reach Western markets through indirect routes including the Gulf and Turkish trade hubs. Buyers should expect clear documentation of country of origin and treatment status.

Position relative to other sources

The principal alternative sources of high-quality turquoise in modern trade are the United States, particularly Arizona and Nevada, and historically Sinai. Khorasan retains a particular cultural and historical prestige that supports premium pricing for top-grade material. For the working trade Khorasan turquoise is the reference point against which other turquoise sources are still judged, even where contemporary supply patterns favour American material on availability grounds.