title: Is the mineral borickyite (Ca,Mg)(Fe3+,Al)4(PO4,SO4,CO3)(OH)(8)·3-7.5H2O the same as delvauxite CaFe4(3+)(PO4,SO4)2(OH)(8)·4-6H2O?
abstract: The two minerals borickyite and delvauxite CaFe(4)(3+)(PO(4),SO(4))(2)(OH)(8)·4-6H(2)O have the same formula. Are the minerals identical or different? The minerals borickyite and delvauxite have been characterised by Raman spectroscopy. The minerals are related to the minerals diadochite and destinezite. Both minerals are amorphous. Delvauxite appears to vary in crystallinity from amorphous to semi-crystalline. The minerals are often X-ray non-diffracting. The minerals are found in soils and may be described as 'colloidal' minerals. Vibrational spectroscopy enables an assessment of the molecular structure of borickyite and delvauxite. Bands are assigned to phosphate and sulphate stretching and bending modes. Multiple water bending and stretching modes imply that non-equivalent water molecules in the structure exist with different hydrogen bond strengths. The two minerals show differing spectra and must be considered as different minerals.
authors.affiliation: Chemistry Discipline, Faculty of Science and Technology, Queensland University of Technology, Brisbane, Queensland 4001, Australia. r.frost@qut.edu.au
authors.forename: Ray L
authors.initials: RL
authors.lastname: Frost
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Palmer
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Xi
mesh_terms: D000535:Aluminum / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013431:Sulfates / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D008903:Minerals; D010710:Phosphates; D013431:Sulfates; D014867:Water; D000535:Aluminum; D007501:Iron; D008274:Magnesium; D002118:Calcium