Abstract

Oxo-mangano-leakeite, a newly approved end-member of the amphibole supergroup (IMA-CNMNC 2015-035), has been found in a rock containing manganese silicate and oxide at the Hoskins Mine, a Mn deposit 3 km west of Grenfell, New South Wales. The end-member formula of oxo-mangani-leakeite is ANaBNa2C(MforumlaLi )TSi8 O22WO2, which would require SiO2 53.15, Mn2O3 34.91, Li2O 1.66, Na2O 10.28, total 100.00 wt.%. The empirical formula derived for the sample of this work from electron and ion microprobe analysis using constraints resulting from single-crystal structure refinement is A(Na0.65K0.36)Σ=1.01B(Na1.94Ca0.06)Σ=2.00C(Mg1.60Zn0.01MforumlaFforumlaAl0.03Tforumla Li0.58)Σ=5.01T(Si7.98Al0.02)Σ=8.00O22W(O1.34OH0.66)Σ=2.00. Oxo-mangano-leakeite is biaxial (–), with α = 1.681, β = 1.712, γ = 1.738, all ± 0.002, and 2V (meas.) = 81.0(4)°, 2V (calc.) = 83.5°. The unit-cell dimensions are a = 9.875(5), b = 17.873(9), c = 5.295(2) Å, β = 104.74(3)°, V = 903.8 (7) Å3; the space group is C2/m, with Z = 2. The strongest ten reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.423, 100, (110); 3.377, 46, (131); 4.461, 40, (040); 4.451, 40, (021); 3.134, 37, (310); 2.694, 37, (151); 2.282, 27, (forumla12); 2.734, 25, (forumla31); 2.575, 24, (061); 2.331, 24, [(forumla51) (forumla21)]. The holotype material is deposited in the Canadian Museum of Nature, Ottawa, under the catalogue number CMNMC 86895.

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