2010/12/01 by Francesco Demartin, Carlo Castellano, C. M. Gramaccioli +1 · 2 citations
Materials Science · Chemistry · #X-ray Diffraction in Crystallography #Crystal Structures and Properties #Inorganic Fluorides and Related Compounds
paper · doi:10.3749/canmin.48.5.1465
openalex publication_date 2010/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/07
Aluminocoquimbite, AlFe(SO 4 ) 3 ·9H 2 O, is a new mineral species formed as a product of low-temperature ( P 31 c (no. 163), with a 10.7065(7), c 17.3077(11) A, V 1718.2(2) A 3 and Z = 4. The strongest six reflections in the X-ray powder-diffraction pattern [ d obs in A( I )( hkl )] are: 9.251(100)(010), 5.310(83)(110), 3.152(43)(224), 4.087(33)(022), 1.765(20)(553), and 2.112(17)(251). Chemical analyses yielded the empirical formula Al 1.07 Fe 0.92 S 2.92 H 18.49 O 21 . The simplified formula is AlFe(SO 4 ) 3 ·9H 2 O. The measured density is 2.03(1) g/cm 3 , and the calculated density is 2.044 g/cm 3 . The mineral is uniaxial (+), with ω = 1.53 and e = 1.56 (589 nm). Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0218, and wR 2 = 0.0685. The structure of aluminocoquimbite is different from that of coquimbite, and contains isolated Al(H 2 O) 6 octahedral units and infinite [Fe(SO 4 ) 3 ] ∞ columns running along [001], consisting of octahedrally coordinated iron atoms and sulfate ions, similar to those observed in ferrinatrite, Na 3 (H 2 O) 3 [Fe(SO 4 ) 3 ]. Interstitial H 2 O molecules are arranged in a cyclohexane-like chair conformation held together by hydrogen bonding, as in the structure of coquimbite.