jadeite, fei cui, Russia, Polar Urals, gems

New additional data on petrography and mineralogy of jadeite and associated rocks from the Polar Urals and Prebalkhash region are given. Some questions of the jadeite rock genesis in hyperbasites are also considered. In the Pay-Yer massif, Polar Urals, the jadeite rocks are associated with a gabbro–pyroxenite complex, garnet-bearing gabbro–amphibolite, metamorphic schists, and glaucophane rocks. Jadeitite and albitite form a chain of lens-shaped bodies in hyperbasites and represent metasomatic metagabbro rocks, altered under conditions of high pressure and high soda potential. Secondary processes of diaphthoresis are strongly revealed. In the Kantegir hyperbasite massif, northern Prebalkhash region, jadeitites form drop-like bodies together with numerous inclusions of unaltered granitoids and other metasomatic rocks. Jadeitite and hornblende are the earliest (high-temperature) metasomatic rocks. Chemical, optical, and X-ray data of jadeitite and accessory and other minerals of jadeite rocks are given. The authors conclude that jadeite rocks of the Polar Urals formed at a temperature close to 700 °C and at a general pressure not less than 14,000 bars; the Prebalkhash jadeite, at a temperature close to 600 °C and pressure not less than 12,000 bars. High pressure is caused by stress produced in deep fault zones. The Na₂O potential and partial pressure of H₂O are of great importance, a question discussed in the light of the most recent data. The prevailing type of formation process (mechanism) of jadeite rocks in hyperbasites is bimetasomatos, which is not always accompanied by desilication. Composition and genesis of original rocks is not of decisive significance. Appropriate model and genetic features of the mentioned deposits are considered in this paper.