Ferriphoxite and carboferriphoxite: two new oxalato–phosphate minerals from the Rowley mine, Arizona, USA

Abstract Ferriphoxite, [(NH 4 ) 2 K(H 2 O)][Fe 3+ (HPO 4 ) 2 (C 2 O 4 )], and carboferriphoxite, [(NH 4 )K(H 2 CO 3 )][Fe 3+ (HPO 4 )(H 2 PO 4 )(C 2 O 4 )], are new mineral species from the Rowley mine, Maricopa County, Arizona, USA. They occur with antipinite, aphthitalite, baryte, fluorite, hematite and quartz in an unusual bat-guano-related, post-mining assemblage. Ferriphoxite occurs as rectangular blades, up to ∼0.1 mm in length, typically forming sprays. Carboferriphoxite occurs as needles or blades, up to ∼0.2 mm in length, typically forming fan- and bowtie-like sprays. Both species are colourless with white streak, vitreous lustre, ∼2 Mohs hardness, brittle tenacity and splintery fracture. Ferriphoxite has three good cleavages ({100}, {010} and {001}) and carboferriphoxite has two good cleavages (probably {100} and {001}). Both species have a measured density of 2.14(2) g·cm –3 . Ferriphoxite is biaxial (+) with α = 1.524(3), β = 1.560(3), γ = 1.608(3) and 2V meas. = 83.9(4)°. Carboferriphoxite is biaxial (+) with α = 1.525(3), β = 1.555(calc), γ = 1.630(3) and 2V meas. = 67(1)°. Electron probe microanalysis gave {[(NH 4 ) 2.13 K 0.87 ] Σ3.00 (H 2 O)} {(Fe 3+ 0.95 Al 0.05 ) Σ1.00 (HPO 4 ) 2 (C 2 O 4 )} for ferriphoxite and {[(NH 4 ) 1.12 K 0.88 ] Σ2.00 (H 2 CO 3 )} {(Fe 3+ 0.78 Al 0.22 ) Σ1.00 (HPO 4 )(H 2 PO 4 )(C 2 O 4 )} for carboferriphoxite. Ferriphoxite is monoclinic, P 2 1 / c , with a = 11.389(5), b = 6.352(3), c = 18.716(9), β = 102.887(9)°, V = 1319.8(11) Å 3 and Z = 4. Carboferriphoxite is triclinic, P $\bar 1$ , with a = 6.4405(3), b = 9.399(5), c = 11.839(6) Å, α = 95.763(10), β = 92.314(10), γ = 100.665(8)°, V = 695.6(6) Å 3 and Z = 2. The structures of ferriphoxite ( R 1 = 0.0678 for 1850 I > 2σ I reflections) and carboferriphoxite ( R 1 = 0.0427 for 3602 I > 2σ I reflections) both contain double-strand chains of corner-sharing Fe 3+ O 6 octahedra and PO 3 (OH) tetrahedra. The chain in ferriphoxite is decorated by PO 3 OH tetrahedra and C 2 O 4 groups and that in carboferriphoxite is decorated by PO 2 (OH) 2 tetrahedra and C 2 O 4 groups. The interstitial units in both structures contain K + and NH 4 + cations along with a H 2 O group in ferriphoxite and an H 2 CO 3 group in carboferriphoxite.