Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Tait, K. T. Articles by Hawthorne, F. C. Search for Related Content GeoRef GeoRef Citation

JOHILLERITE FROM TOLBACHIK, KAMCHATKA PENINSULA, RUSSIA: CRYSTAL-STRUCTURE REFINEMENT AND CHEMICAL COMPOSITION

Kimberly T. Tait^¶ and Frank C. Hawthorne

Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada

E-mail address: frank_hawthorne{at}umanitoba.ca

Johillerite from a fumarole in the North Breach of the Great Fissure Tolbachik eruption (GFTE), Kamchatka Peninsula, Russia, monoclinic, a 6.7520(14), b 12.739(3), c 11.068(2) Å, ß 100.37(3)°, V 936.4(2) ų, I2/a, Z = 4 has been refined to an R₁ value of 3.2% for 1175 observed (|F_o| 4F) reflections measured with a Bruker P4 diffractometer equipped with a CCD detector. The crystal used for the collection of the X-ray intensity data was subsequently analyzed with an electron microprobe; the resulting structural formula is Na_0.77 K_0.03 Pb_0.01 Ca_0.01 Mn_0.01 ²⁺ Zn_0.13 Mg_2.18 Cu_1.55 ²⁺ Fe_0.26 ³⁺ Al_0.06 (As_2.96 ⁵⁺ P_0.04) O₁₂. The unusual feature of the johillerite structure is the A(1)’ site, a square-planar-coordinated site fully occupied by Cu²⁺, that is displaced along x. The A(2) site is similar to that in other alluaudite-group minerals, surrounded by eight O-atoms with a <A(2)–O> distance of 2.70 Å, and occupied by Na plus small amounts of other large cations. The refined site-scattering values and observed <M–O> distances at the M(1) and M(2) sites are in accord with occupancy primarily by Mg, with Cu²⁺ at M(1) and Cu²⁺ + Fe³⁺ + Al at M(2). Relative to the compositions of the arsenate minerals arseniopleite and caryinite, Cu²⁺ has replaced Ca in the formula of johillerite. In arseniopleite and caryinite, Ca (+ Na) at the A(1) site is [7]- or [8]-coordinated, and the resulting sites occur in chains of edge-sharing coordination polyhedra extending in the a direction. Rather than replacing Ca at the center of the A(1) polyhedron, Cu²⁺ in johillerite occurs close to the edge shared between adjacent polyhedra, adopting square-planar coordination that is common for Cu²⁺.

Keywords: johillerite, crystal structure, alluaudite group, Cu mineral, Kamchatka, Russia.