• journal_title：The Canadian Mineralogist
• Contributor：Mark A. Cooper ; Frank C. Hawthorne ; Yassir A. Abdu ; Neil A. Ball ; Robert A. Ramik ; Kimberly T. Tait
• Publisher：Mineralogical Association of Canada
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.51.1.93
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：51
• issue：1
• firstpage：93
• section：Article

Wopmayite, ideally Ca₆Na₃□Mn(PO₄)₃(PO₃OH)₄, is a new secondary mineral from the Tanco mine, Bernic Lake, Manitoba. It occurs in vugs in a single 5–10 cm mass of phosphate-carbonate mineralization in a spodumene-rich boulder found in the dumps of the Tanco Mine, Bernic Lake, Manitoba, Canada. It is a secondary mineral that crystallized together with rhodochrosite, quartz, whitlockite, apatite, and other phases after dissolution of primary lithiophosphate by hydrothermal solutions. The initial crystal of wopmayite was a corroded {101̅1} rhomb ∼150 microns across. Wopmayite is colorless to white to pale pink with a white streak and a vitreous luster, and does not fluoresce under ultraviolet light. It has a Mohs hardness of 5, is brittle, has an irregular to subconchoidal fracture, and shows no cleavage or parting. The calculated density is 3.027 g/cm³. It is uniaxial (-), ω = 1.617, ɛ = 1.613, both ± 0.002. Wopmayite is hexagonal-rhombohedral, space group R3c, a 10.3926(2), c 37.1694(9) Å, V 3476.7(2) ų, Z = 6, a:c = 1:3.577. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I, (h k l): 2.858, 100, (02.10); 3.186, 88, (2̅34); 2.589, 68, (2̅40); 5.166, 33, (1̅20); 6.421, 32, (1̅14); 8.017, 31, (012); and 3.425, 29, (1̅110). Chemical analysis by electron microprobe gave P₂O₅ 46.40, Al₂O₃ 0.38, Fe₂O₃ 0.80, FeO 0.96, MnO 3.74, MgO 0.41, CaO 37.65, SrO 0.91, Na₂O 5.43, and H₂O(calc) 2.00, sum 98.68 wt.%. The H₂O content was determined by crystal-structure analysis. On the basis of 28 O apfu, the empirical formula is (Ca₇.19 Na_1.88 Sr_0.09)_Σ9.16(Mn_0.56 Mg_0.11Fe²⁺_0.14 Fe³⁺_0.11Al_0.08)_Σ1.00(PO₄)_4.63(PO₃OH)_2.37, and the endmember formula is Ca₆Na₃□Mn(PO₄)₃(PO₃OH)₄.

The crystal structure of wopmayite was solved by direct methods and refined to an R₁ index of 2.21% based on 2288 unique observed reflections collected on a three-circle rotating-anode (MoKα X-radiation) diffractometer equipped with multilayer optics and an APEX-II detector. Wopmayite has a structural unit consisting of an [M²⁺(PO₄)₆] arrangement that is topologically the same as the structural units in the whitlockite and merrillite structures. The [M²⁺(PO₄)₆] clusters are linked by Ca polyhedra and (PO₃Φ) groups of the form {Ca₉X(PO₃Φ)} where Φ = O,OH and X = (□, Na, Ca), depending on the mineral species. Wopmayite is related to whitlockite by the substitution Na + H → Ca + □, whereby Na is incorporated primarily at the Ca(3) site and H attaches to the P(1) tetrahedron to produce an acid-phosphate group. Thus merrillite contains no acid-phosphate group, whitlockite contains a single acid-phosphate group at P(3), and wopmayite contains acid-phosphate groups at both P(1) and P(3).