Pakhomovskyite, Co3(PO4)2•8H2O, a new mineral species from Kovdor, Kola Peninsula, Russia

Pakhomovskyite, Co-3(PO4)(2)center dot 8H(2)O, is a new mineral species found in dolomite carbonatite Cutting phoscorites in the Iron-Ore Complex. Kovdor. Kola Peninsula, Russia. The mineral was found as groups (up to 3 X 2 cm) of small spherulites (up to 0.5 mm diameter) and rosettes (up to 0.05 mm diameter) of well-shaped tabular crystals growing on walls of leached fissures in dolomitic carbonatite. The associated minerals are bakhchisaraitsevite, bobierrite, magnetite, kovdorskite, rimkorolgite, juonniite, norsethite. chalcopyrite, phlogopite, pyrrhotite and pyrite. Pakhomovskyite is bright pink, with a dull luster in aggregates, and pearly luster in separate flakes. The streak is pink. The spherulites are translucent, non-fluorescent. The Mobs hardness is about 2. The mineral is flexible in thin flakes. Cleavage is perfect on {010}, and the fracture is stepped. Density is 2.71(2) g/cm(3) (measured using heavy liquids) and 2.71 g/cm(3) (calculated). Pakhomovskyite is biaxial (+), alpha 1.581(2), beta 1.600(2), gamma 1.631(2) (589 nm), 2V (meas.) 75-80 degrees, 2V(calc.) 77 degrees. The dispersion is weak, r < v. Optical orientation: X = b, Y boolean AND c in the range 22-23 degrees in the obtuse beta angle. with pleochroism from pale pink on Y to pinkish grey on Z. Chemical analysis with in electron microprobe gave (wt%): CoO 34.88, MgO 2.97, MnO 2.41. FeO 0.40, NiO 0.53, P2O5 27.95 H2O (by the Penfield method) 29.50, total 98.64. The empirical formula calculated on the basis of Co+Mg+Mn+Ni+Fe+P = 5 is (Co2.38Mg0.38Mn0.17Ni0.04Fe003)Sigma 2.992+ (PO4)(2.01)center dot 8.35H(2)O. The simplified formula is Co-3(PO4)(2)center dot 8H(2)O. According to X-ray-diffraction studies, pakhomovskyite is monoclinic, C2/m a 10.034(4) b 13.341(3), c 4.670(3) angstrom, beta 105.02(2)degrees, V 603.8 angstrom(3). Z = 2. The strongest six lines in the X-ray powder-diffraction pattern [d(obs)(angstrom)(I-obs)hkl] are: 6.67(100)(020), 3.195(60)(1 (3) over bar1), 2.948(70)(31 (1) over bar), 2.691(70)(221), 2.521(60)(241) 2.408(60)(40 (1) over bar). Pakhomovskyite. a new member of the vivianite group, is an analogue of synthetic Co-3(PO4)(2)center dot 8H(2)O. Pakhomovskyite is the latest low-temperature hydrothermal mineral to form, as a result of dissolution of primary ore minerals by alkaline phosphate-bearing solutions. The mineral is named in honor of Yakov A. Pakhomovsky, who has made significant contributions to the mineralogy of the alkaline massifs of the Kola Peninsula.