Synchrotron radiation diffraction study of the mineral moolooite, and synthetic copper oxalates

The orthorhombic mineral moolooite, CuC2O4. nH2O, described by Clarke and Williams (1986) using Debye-Scherrer photographic data, has a fully-disordered stacking fault (FDSF) structure. Related monoclinic models have been reported for various synthesised samples based on Schmittler (1968). In the present study, synchrotron radiation diffraction data for moolooite and synthesised specimens have been examined with particular reference to crystallographic disorder. The moolooite data correspond to space group Pnnm, with a = 5.3064(2), b = 5.6804(2), c = 2.5630(1) Å; Vc = 77.26(1) Å3; and Z = 1; and the FDSF structure along the b-direction has been confirmed. The synthetic specimen data from the study indicate partial ordering, with space group P21/n; and the cell parameters for one specimen being a = 5.957(7), b = 5.611(5), c = 5.133(7) Å; β = 115.16(2)°; Vc = 155.27 Å3 and Z = 2. The level of zeolitic water in the materials has been considered using the approach of Schmittler based on thermogravimetry and pycnometry. The new data for natural topotype material correspond to CuC2O4.1.0H2O. It is postulated that the level of water for natural and synthetic specimens may be attributed to the conditions under which the material forms.

Zeolitic water in strunzite-group minerals

ABSTRACTThe crystal structures have been refined for the first time for the strunzite-group minerals ferristrunzite and ferrostrunzite. Structure refinements are also presented for strunzite from three different localities. A common feature of all refined structural models is the presence of zeolitic water in the interlayer region, displaced by 0.4–0.5 Å from an inversion centre at (½ 0 ½). The refined occupancy of the site ranged from 44% to 100% in the samples studied. H-bonding associated with the zeolitic water causes large displacements, up to 0.7 Å, of neighbouring coordinated water molecules, relative to the structure with no zeolitic water. A new formula is proposed for strunzite-group minerals with divalent interlayer cations as M2+ Fe23+(PO4)2(OH)2·(6.5–x)H2O where M = Mn, Fe or Zn, and 0 < x < 0.5 accounts for varying degrees of dehydration. For ferristrunzite and other potential strunzite-group members with trivalent cations in the interlayer octahedron, the formula is M3+ Fe23+ (PO4)2(OH)3·(5.5–x)H2O.

Crystal chemistry of zinc incorporation in strunzite-group minerals containing zeolitic water

A comparative study is presented of the chemistry and crystallography of zinc-bearing strunzites from Hagendorf Süd, Bavaria, Germany and the Sitio do Castelo mine, Folgosinho, Portugal. Electron microprobe analyses of samples from the two localities show quite different cation substitutions. The Hagendorf Süd mineral is a Zn-bearing ferristrunzite, with compositional zoning due to Zn2+ replacing predominantly Fe3+ as well as minor Mn2+, whereas the Portugese mineral is a Zn-bearing strunzite, in which Zn2+ replaces Mn2+, with minor replacement of Fe3+ by Mn3+. Zincostrunzite, with dominant Zn in the interlayer octahedrally coordinated site, is a new strunzite-group mineral that has been characterized at both locations. Analysis of single-crystal synchrotron data for zinc-bearing ferristrunzite and zincostrunzite crystals from Hagendorf Süd show that the structures of both minerals contain zeolitic water in the interlayer region. The formula for strunzite-group minerals containing the zeolitic water is MFe23+(PO4)2(OH)2·6.5H2O, M=Fe, Mn, Zn. This formulation agrees with that found for zincostrunzite from the Sitio do Castelo mine, but differs from that reported previously for strunzite, MFe2+(PO4)2(OH)2·6H2O, which has no interlayer water. Interestingly, the zincostrunzites from the two localities differ in the location of the interlayer water molecule, with a corresponding difference in the H bonding.

Insertion of acetone molecules in the nanostructured tunnels of palygorskite

The insertion of acetone molecules in the nanostructured tunnels of palygorskite (PFl-1) was studied by thermal gravimetric analysis connected with mass spectrometry and 29Si and 13C solid-state NMR techniques. In comparison with palygorskite, new weight losses appear at 130 and 340 °C for palygorskite previously heated at 150 °C for 20 h then exposed to acetone for a week. Two types of water molecules occupy the palygorskite tunnels: weakly bound zeolitic water and structural water molecules coordinated to Mg(II) cations at the edge of the octahedral sheets. Acetone molecules that intercalate in the nanostructured tunnels replace the zeolitic water and are H-bonded to structural water. The mass loss at 130 °C is accounted for by the release of structural water and acetone. The loss at 340 °C is due to the release of acetone molecules that coordinate directly to terminal cations in the nanostructured tunnels and to residual structural water. A nanostructured hybrid material, with a structure similar to the parent palygorskite, can be formed through the direct coordination of acetone molecules to the terminal cationic coordination sites in the nanostructured tunnels of palygorskite. There is evidence for the fixation of two different types of acetone on palygorskite: mobile acetone molecules on the external surface and acetone molecules more rigidly fixed inside the nanotunnels. The former ones are detected by the 13C magic-angle spinning NMR experiment and can be easily removed by gentle heating at 60 °C, while the latter ones are detected by 13C cross-polarization magic-angle spinning NMR. It is also demonstrated that nearly complete recovery of the original structure is achieved by exposing palygorskite previously dehydrated at 150 or 300 °C to acetone vapor at room temperature. Key words: insertion, intercalation, nanostructured tunnels, palygorskite, acetone, nanocomposite materials, nanohybrid.

Données nouvelles sur la laumontite de la zone métamorphique de Libramont, Belgique [New mineralogical data on laumontite from the metamorphic zone of Libramont, Belgium]

New laumontite occurrences have been discovered at Bertrix, Ochamp and Luchy, in the metamorphic zone of Bastogne-Libramont. Wet chemical analyses lead to compositions close to Ca[Al2Si4O12].4H2O, with a slightly variable water content and a significant amount of potassium (up to 0.76% K2O). Infrared spectra show an ordered distribution of tetrahedral Si and Al, and relatively low hydrogen bonds between zeolitic water and crystal freamework. Laumontite crystallized in rocks fractures, under a presure lower than 3 kbar and a temperature between 170 and 280°C. The presence of albite in quartz veins and of laumontite in rocks fissures indicates a different geochemical behaviour for Na and Ca during this retrometamorphic phase.