The crystal structure of Ba2F2(S6+O3S2-), a natural thiosulphate weathering product of old smelting slags at the Surrender Mill, Yorkshire, England, UK, has been solved to R1 = 0.88% for 399 unique [Fo > 4 σ F] reflections and 0.91% for all 407 reflections. The compound is monoclinic, C2/m, a 15.3172(5), b 4.5898(1), c 4.6320(2) Å, β 101.449(1)°, V 319.17(2) Å3. The structure of Ba2F2(S6+O3S2-) consists of BaF2Ba layer fragments of the fluorite-type structure of frankdicksonite (BaF2) parallel to (100) alternating with layers of thiosulphate groups. The layer sequence in one unit cell is (S6+O3S2-)-BaF2Ba-(S6+O3S2-)-BaF2Ba. The structure resembles that of grandreefite, Pb2F2SO4.

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