• journal_title：The Canadian Mineralogist
• Contributor：T. Scott Ercit ; Kimberly T. Tait ; Mark A. Cooper ; Yassir Abdu ; Neil A. Ball ; Alan J. Anderson ; Petr Černý ; Frank C. Hawthorne ; Miguel Galliski
• Publisher：Mineralogical Association of Canada
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.48.5.1455
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：48
• issue：6
• firstpage：1455
• section：Articles

Manitobaite, ideally Na₁₆ Mn²⁺₂₅ Al₈ (PO₄)₃₀, is a new mineral species from Cross Lake, Manitoba, Canada. It occurs as large crystals or cleavage masses intergrown with other phosphate minerals in a phosphate pod in the intermediate and core zones of pegmatite #22 on the southeastern shoreline of a small unnamed island in Cross Lake, Manitoba, about 5 km north–northwest of the Cross Lake settlement, longitude 54° 41′ N, latitude 97° 49′ W. Associated minerals are fluorapatite, chlorapatite, bobfergusonite, eosphorite, dickinsonite, fillowite, triploidite, goyazite, perloffite, beusite, triplite, as well as quartz, K-feldspar, muscovite, schorl, beryl, spessartine, gahnite and (Nb,Ta,Sn) oxides. Manitobaite is opaque in large crystals (up to 4 cm), and transparent to translucent in small (<1 mm) grains. Color varies from green to brown, with a colorless to very pale green or very pale greenish brown streak and a vitreous to resinous luster; manitobaite does not fluoresce under ultraviolet light. The cleavage is perfect on {010}, there is no parting, the tenacity is brittle, and the fracture is hackly. The following properties were measured on the green variety of manitobaite. The measured and calculated densities are 3.621(6) and 3.628 g cm⁻³, respectively. Manitobaite is biaxial negative with α 1.682, β 1.691, γ 1.697 (all ±0.001), with X ∧ a = 31.7° (in β obtuse), Y || b, Z ∧ c = 20.2° (in β acute); 2V_obs = 78.1(6)°, 2V_calc = 77.9°. It is pleochroic X = orange brown, Y = green, Z = greenish brown, with absorption Y ≥ Z > X and dispersion r > v, medium. Manitobaite is monoclinic, Pc, a 13.4516(15), b 12.5153(16), c 26.661(3) Å, β 101.579(10)°, V 4397.1(6) ų, Z = 2, a:b:c = 1.07482:1:2.13027. The strongest seven lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 2.715(100)(242), 2.730(50)(404), 3.494(47)(313), 3.078(27)(3̅17), 2.518(22)( 5̅15), 2.881(21)(1̅19), and 6.260(20)(020). A chemical analysis with an electron microprobe gave P₂O₅ 44.19, Al₂O₃ 6.91, FeO 7.79, MnO 27.57, ZnO 0.54, MgO 0.73, CaO 1.71, Na₂O 9.97, for a total of 99.58 wt%. The resulting empirical formula, using the valence states of Fe determined by Mössbauer spectroscopy, is Na_15.55 Ca_1.47 Mg_0.88 Fe²⁺_4.19 Mn²⁺_18.78 Zn_0.32 Al_6.54 Fe³⁺_1.05 P_30.08 O₁₂₀ based on 120 O²⁻ anions pfu. The general formula is (Na,Ca,□)₁₆ (Mn²⁺,Fe²⁺,Ca,Al,Fe³⁺,Mg,Zn)₂₅ (Al,Fe³⁺,Mg,Mn²⁺, Fe²⁺)₈ (PO₄)₃₀, and the end-member formula is Na₁₆ Mn²⁺₂₅ Al₈ (PO₄)₃₀. The crystal structure of manitobaite is an ordered superstructure of the alluaudite arrangement with a cell volume five times that of alluaudite.