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Carlfrancisite, Mn 3  2+ (Mn 2+ ,Mg,Fe 3+ ,Al) 42 (As 3+ O 3 ) 2 (As 5+ O 4 ) 4 [(Si,As 5+ )O 4 ] 6 [(As 5+ ,Si)O 4 ] 2 (OH) 42 , is a new mineral from the Kombat mine, Otavi Valley, Namibia, and occurs as curved platy aggregates ~2 cm across on a matrix of Mn arsenates and oxides. It is yellowy orange to pale yellow with a very pale-yellow streak, translucent with a vitreous to opalescent luster, and does not fluoresce under ultraviolet light. Cleavage is micaceous on {001}, and no parting or twinning was observed. Mohs hardness is 3, and carlfrancisite is brittle with a hackly fracture. The calculated density is 3.620 g/ cm 3 . Optical properties were measured with a Bloss spindle stage for the wavelength 590 nm using a gel filter. The indices of refraction are e = 1.756, w = 1.758, and it is non-pleochroic. Carlfrancisite is trigonal, space group R3̄c, a = 8.2238(2), c = 205.113(6) Å, V = 12 013.5(4) Å 3 , Z = 6, c:a = 1:24.941. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: d (Å), I, (hkl): 2.826, 100, (2̄ 2 44); 2.371, 88, (2̄ 3 40, 1̄ 3 41); 1.552, 84, (1̄ 5 0); 2.676, 63, (2̄ 3 7); 3.243, 54, (0 1 56, 1̄ 2 39); 4.107, 48, (1̄ 2 0); 2.918, 47, (0 2 40). Chemical analysis by electron microprobe and crystalstructure refinement gave As 2 O 5  13.07, As 2 O 3  3.18, P 2 O 5  0.50, V 2 O 5  0.74, SiO 2  8.96, Al 2 O 3  0.78, FeO 0.22, MnO 53.25, MgO 9.37, H 2 O(calc) 8.42, sum 98.49 wt%. The H 2 O content and the valence states of As were determined by crystal-structure analysis. The empirical formula is Mn 2+   33.55 Mg 10.39 Fe 2+  0.14 Al 0.68  As 3+  1.44 (Si 6.67 P 0.32 V 5+   0.37 As 5+  5.08 )O 54  (OH) 42  on the basis of 96 anions with (OH) = 42 apfu. The structure of carlfrancisite is closely related to that of mcgovernite and turtmannite.

american mineralogist

Carlfrancisite: Mn 3   2+ (Mn 2  + ,Mg,Fe 3+ ,Al) 42 (As 3+ O 3 ) 2 (As 5+ O 4 ) 4 [(Si,As 5+ )O 4 ] 6 [(As 5+ ,Si)O 4 ] 2 (OH) 42 , a new arseno-silicate mineral from the Kombat mine, Otavi Valley, Namibia