The crystal structure of meurigite, ideally [K(H 2 O) 2.5 ][Fe 8 3+ (PO 4 ) 6 (OH) 7 (H 2 O) 4 ], monoclinic, C2/c, a = 29.018(5), b = 5.1892(6), c = 19.695(3) Å, β = 106.987(1)°, Z = 4, from the Santa Rita mine, New Mexico, has been solved and refi ned to R 1 = 4.69%, wR 2 = 12.6% using 3325 unique [F o > 4σ(F o )] refl ections collected using a Bruker 6000 SMART CCD diffractometer and synchrotron radiation of wavelength 0.41328 Å. The structure of meurigite is a framework consisting of face-sharing octahedral Fe 2 3+ O 9 dimers, which are linked by sharing corners with corner-sharing dimers and isolated Fe 3+ O 6 octahedra to form thick slabs of octahedra parallel to the a-c plane. PO 4 tetrahedra further link octahedra within the slabs and also link slabs to one another perpendicular to the a-c plane. Relatively large channels through the framework along the b axis contain disordered K atoms and H 2 O molecules, which take part in two overlapping arrays. Partial vacancies in the Fe and P sites may account for discrepancies between the empirical and ideal chemical formulas. Packing considerations suggest that the empirical formula should be based on the total number of large ions (K + Na + O = 38.5 per formula unit), which for the chemical analysis provided in the original description yields [(K 0.91 Na 0.03 ) Σ0.94 (H 2 O) 2.56 ] Σ3.50 [(Fe 3+ 7.52 Al 0.17 Cu 0.03 ) Σ7.72 (PO 4 ) 5.48 (CO 3 ) 0.21 (OH) 7.20 (H 2 O) 5.23]. The meurigite structure is related to those of other fi brous ferric phosphates with 5 Å fi ber axes and shows a particularly close relationship with the structure of dufrénite. Crystal chemical evidence suggests that, even if meurigite and phosphofi brite are isostructural, phosphofi brite may qualify as a distinct species based upon its low K content (<0.5 apfu based on a recalculation of the original chemical analysis).