Original paper

Structure solution from powder data of the phosphate hydrate tinticite

Rius, Jordi; Louër, Daniel; Louër, Michèle; Galí, Salvador; Melgarejo, Joan Carles

European Journal of Mineralogy Volume 12 Number 3 (2000), p. 581 - 588

13 references

published: May 31, 2000
manuscript accepted: Jan 19, 2000
manuscript received: Jul 26, 1999

DOI: 10.1127/0935-1221/2000/0012-0581

BibTeX file

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Abstract The crystal structure of the mineral tinticite has been solved by direct methods from integrated intensities of X-ray powder diffraction data and subsequently refined with the Rietveld technique. The sample used for the structure solution comes from the Gavá-Bruguers area (20 km SW of Barcelona), which contains a large variety of phosphates, some of which were exploited in gallery mines during the ancient neolithic. Tinticite crystallizes in the triclinic space group P1 with unit cell parameters a = 7.965(2) Å, b = 9.999(2) Å, c = 7.644(2) Å, α = 103.94(2)°, β = 115.91(2)°, γ = 67.86(2)° and cell content Fe3+5.34(PO4)3.62(VO4)0.38(OH)4·6.7 H2O; pexp = 2.94 g/cm3; = 2.88 g/cm3. The Rietveld refinement of the data set converged to = 13.1 % and Χ = 3.3. Due to the complexity of the disorder in this structure, the refined structure model could only account for part of it. The octahedrally coordinated Fe3+ ions form dreier single chains of general formula ∞1[Fe3O14] at y = 0 and trimers of type cis-[Fe3O14] placed at y = 1/2. While the dreier single chains are linked to each other by fully occupied PO4 groups yielding in this way pre- dominantly ordered layers, the trimers are partially disordered and connected to each other and to the ordered layers both by PO4 groups and through H-bonds. The higher stability of the ordered layers is consistent with the observed platy nature of the microcrystals of tinticite


tinticitephosphate hydratemineralab initio structure determinationpowder diffractionRietveld analysisdirect methods