503 § Permanent address: Department of Crystallography, St. Petersburg State University, St. Petersburg 199034, Russia. E-mail address: skrivovi@mail.ru. Current mailing address: Mineralogisch-Petrographisches Institut, Christian-Albrechts- Universität Kiel, Olshausenstrasse 40, D-24118 Kiel, Germany. The Canadian Mineralogist Vol. 41, pp. 503-511 (2003) CHLORBARTONITE, K 6 Fe 24 S 26 (Cl,S), A NEW MINERAL SPECIES FROM A HYDROTHERMAL VEIN IN THE KHIBINA MASSIF, KOLA PENINSULA, RUSSIA: DESCRIPTION AND CRYSTAL STRUCTURE VICTOR N. YAKOVENCHUK AND YAKOV A. PAKHOMOVSKY Geological Institute, Kola Science Centre of the Russian Academy of Sciences, Apatity 184200, Russia YURY P. MEN’SHIKOV Laplandia Minerals Ltd., Apatity 184200, Russia GREGORY YU. IVANYUK Geological Institute, Kola Science Centre of the Russian Academy of Sciences, Apatity 184200, Russia SERGEY V. KRIVOVICHEV § AND PETER C. BURNS Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556-5602, U.S.A. ABSTRACT Chlorbartonite, ideally K 6 Fe 24 S 26 (Cl,S), is a new potassium iron sulfide chloride found as an accessory mineral in a microcline – pectolite – sodalite – aegirine vein within feldspathic urtite at Mount Koashva, Khibina massif, Kola Peninsula, Russia. The mineral occurs as roundish grains up to 2 cm across included in sodalite and natrolite crystals; it is associated with djerfisherite and rasvumite. Chlorbartonite is weakly magnetic, brittle, and has a conchoidal fracture. Cleavage and parting were not observed. Macroscopically, the mineral is opaque, brown-black, with a black streak and submetallic luster. In reflected light, it appears optically isotropic, yellowish brown, and without internal reflections; interpolated values of reflectance (R, %) at the standard wavelengths (nm) are: 10.8 (470), 13.5 (546), 15.1 (589), and 17.2 (650). The hardness VHN 40 is 203–212, average 207 kg/mm 2 ; the Mohs hardness is 4. The density is 3.70 g/cm 3 (measured) and 3.65 g/cm 3 (calculated). The electron-microprobe analysis of six grains gave, as an average composition: S 33.84, Cl 0.99, K 9.62, Fe 54.09, Co 0.04, Cu 0.57, total 99.15 wt.%. The empirical formula calculated on the basis of a total of 57 atoms is K 6.08 (Fe 23.93 Cu 0.22 Co 0.01 ) 24.16 S 26.00 (Cl 0.69 S 0.07 ) 0.76 , which yields an ideal formula of K 6 Fe 24 S 26 (Cl,S). The mineral is tetragonal, I4/mmm, a 10.3810(8), c 20.614(2) Å, V 2221.5(3) Å 3 , Z = 2. The strongest eight lines in the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 9.25(33)(101), 5.97(65)(112), 3.121(45)(312), 2.986(100)(224), 2.380(38)(332), 2.374(57)(316), 1.834(51)(440), and 1.830(82)(408). The crystal structure has been refined to an R1 of 0.020 (447 unique observed reflections with F o ≥ 4F o ). The structure consists of a framework of the Fe 8 S 14 clusters of eight edge-sharing FeS 4 tetrahedra. The framework has large cavities occupied by ClK 6 octahedra. As the name indicates, chlorbartonite is the Cl-dominant analogue of bartonite. Keywords: chlorbartonite, new mineral species, bartonite, Khibina alkaline massif, Kola Peninsula, Russia. SOMMAIRE La chlorbartonite, une nouvelle espèce de sulfure chloruré de potassium et de fer dont la formule idéale est K 6 Fe 24 S 26 (Cl,S), est un minéral accessoire dans une veine à microcline – pectolite – sodalite – aegyrine dans une urtite feldspathique au mont Koashva, complexe alcalin de Khibina, péninsule de Kola, en Russie. La chlorbartonite se présente en grains xénomorphes atteignant deux cm dans des cristaux de sodalite et de natrolite; elle est associée à djerfisherite et rasvumite. Elle est faiblement magnétique, cassante, et possède une fracture conchoïdale. Nous ne décelons aucun clivage ou plan de séparation. Du point de vue macroscopique, le minéral est opaque, brun à noir, avec une rayure noire et un éclat sub-métallique. En lumière réfléchie, la