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

• Published in: Mineralogical magazine 2017-10, Vol.81 (5), p.755-766
• Main Authors: Grey, Ian E, Keck, E, MacRae, C. M, Glenn, A. M, Kampf, Anthony R, Nash, B. P, Mills, S. J
• Format: Article
• Language: English
• Subjects: Bavaria Germany; cations; Central Europe; crystal chemistry; crystal chemistry of strunzites; crystal structure; crystallography of strunzites; electron probe data; Europe; ferristrunzite; Folgosinho Portugal; formula; framework silicates; Germany; granites; Hagendorf; Iberian Peninsula; igneous rocks; metals; Mineralogy; nonsilicates; pegmatite; phosphates; plutonic rocks; Portugal; silicates; Sitio do Castelo Mine; Southern Europe; strunzite; synchrotron radiation; water of crystallization; X-ray diffraction data; zeolite group; zeolitic water in strunzites; zinc; zincostrunzite; Zn-bearing ferristrunzite
• ISSN: 0026-461X; 1471-8022
• DOI: 10.1180/minmag.2016.080.151

A comparative study is presented of the chemistry and crystallography of zinc-bearing strunzites from Hagendorf Sud, 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 Sud 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 Sud 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 MFe3+2 (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, MFe3+2(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.