Eight mineral species in one crystal: unique zonation of polychrome tourmaline from the Krutaya vein (Malkhan pegmatite feld, Transbaikalia, Russia)

Abstract

A unique unusually Mn-rich concentrically zoned polychrome crystal from the cavity of granite pegmatite of the Krutaya vein within the Malkhan pegmatite feld (Transbaikalia) is studied. It consists of six valid and two potentially new mineral species of the tourmaline supergroup. The paper provides the detailed physical, chemical and crystallographic characteristics of minerals. A Mn-richest (up to 9.6 wt. % MnO) dark brown core of the crystal is composed of fuor-tsilaisite, princivalleite and a Mn2+-F-analog of foitite. A greenish yellow intermediate zone consists of Mn-rich fuor-elbaite and darrellhenryite and is followed by a Mn-poor pink zone composed of fuor-rossmanite, rossmanite and their O2--analog. A yellowish green peripheral zone consists of late-generation Mn-bearing fuor-elbaite. The Mn content decreases, while the Li + Al content increases from the center of the dark brown zone to the margin of the crystal approximately to the middle of the pink zone, where the evolution of the tourmaline composition is inverted and this trend becomes opposite. The crystal structure of fuor-tsilaisite is refned on a single crystal extracted from this specimen, R1 = 2.4 %. The mineral is trigonal, space group R3m, a = 15.9595(1), c = 7.14164(7) A, V = 1575.31(3) A3, Z = 3.