Sursassite: hydrogen bonding, cation order, and pumpellyite intergrowth
- Author(s)
- Eugen Libowitzky, Mariko Nagashima, Thomas Armbruster, Tetsuo Minakawa, Masahide Akasaka
- Abstract
The crystal chem. of sursassite, simplified formula Mn2+2Al3Si3O11(OH)3, from six different localities [(1) Falotta, Switzerland, (2) Woodstock, New Brunswick, Canada, (3) Kamisugai, Japan, (4) Kamogawa, Japan, (5) Molinello, Italy, and (6) Gambatesa, Italy] was studied using electron microprobe anal. (EMPA), Fourier transform IR spectroscopy (FTIR), and single-crystal X-ray diffraction methods. The structure has two symmetry independent Mn sites. The Mn1 site is seven coordinated by O and hosts, in addn. to Mn2+, up to 20% Ca, whereas Mn2 has octahedral coordination and is strongly selective for Mn2+. In the simplified formula, three smaller octahedral M sites are occupied by Al. However, M1 also accepts significant amts. of divalent cations, such as Cu, Mg, Fe, and Mn, whereas M2 is occupied exclusively by Al. The unit-cell parameters of sursassite are a = 8.698-8.728, b = 5.789-5.807, c = 9.778-9.812 .ANG., .beta. = 108.879-109.060, V = 465.7-470.0 .ANG.3, the space group is P21/m. Structure refinements converged to R1 values of 2.15-6.62%. In agreement with bond-valence analyses, at least three OH groups, depending on the concn. of divalent cations at M1, are found at the O6, O7, and O11 positions. However, the bond-valence sum at O10 is always low, thus partial hydroxylation is assumed at O10 to maintain charge balance. Owing to the influence of divalent cations at M1 in sursassite the hydrogen-bond systems in sursassite and isostructural macfallite are different. The FTIR spectrum in the region of OH-stretching vibrations is characterized by three strong bands at 3511, 3262, and around 2950 cm-1, the latter being broad. The band at 2950 cm-1 is assigned to strong hydrogen bonds between O6 and O10 (O6O10 = 2.66 .ANG.). Residual difference-Fourier peaks in the refinement of the Kamogawa and Molinello (specimen 1) crystals indicated less than 5% pumpellyite intergrowth.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Universität Bern, Ehime University, Shimane University
- Journal
- American Mineralogist: an international journal of earth and planetary materials
- Volume
- 94
- Pages
- 1440-1449
- No. of pages
- 10
- ISSN
- 0003-004X
- Publication date
- 2009
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 1030 Physics, Astronomy, 105116 Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/2d5b73ee-8fa4-4f9c-a338-1780066988fd