The crystal structure of satterlyite from the Big Fish River area, Yukon Territory, Canada, (Fe0.77Mg0.23)12 (PO3OH)(PO4)5(OH,O)6 (space group P31m, a = 11.355(1), c = 5.0394(5) Å, V = 562.71(9) Å3, Z = 1), has been solved and refined using single-crystal intensity data (Mo Kα X-radiation, CCD area detector, 2320 unique reflections with F0 > 4σ(F0), Rl = 2.15 %). The structure is based upon pairs of face-sharing, distorted (Fe,Mg)O6 octahedra linked by edge-sharing to form double chains along [001]. Each double chain shares ligands with six other double chains to produce a three-dimensional network hosting three unique PO4 tetrahedra which are corner-linked to the (Fe,Mg)O6 octahedra. The two unique (Fe,Mg)O6 octahedra are characterised by different occupancies; Fe:Mg ratios of the M(1) and M(2) sites are 0.838(2):0.162(2) and 0.706(2):0.294(2), respectively. Two H atoms are each bonded to common ligands of the two (Fe,Mg)O6 octahedra. The third, strongly disordered H(3) atom is bonded to the apical O of the P(l)O4 tetrahedron. The H(3) site and possibly both the other two H sites are only partially occupied, and only very weak hydrogen bonds exist. Satterlyite is isostructural with holtedahlite, Mg12(PO3OH,CO3)(PO4)5(OH,O)6. Unlike in natural holtedahlite, there is no carbonate-for-phosphate substitution in the satterlyite investigated, which was also confirmed by IR absorption powder spectra. A structural relationship exists with phosphoellenbergerite, Mg14(PO4)6(PO3OH)2(OH)6. Polarised IR spectra of oriented cut single crystals in the O-H stretching vibrational range revealed an asymmetric band at 3536 cm-1 (including a weak shoulder at ∼ 3568 cm-1) and an asymmetric band at ∼ 3471 cm-1. The number of hydroxyl vibrational bands and their positions are in accordance with the results of the structure refinement.

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