- journal_title：Mineralogical Magazine
- Contributor：A. Guastoni ; F. Nestola ; G. Mazzoleni ; P. Vignola
- Publisher：Mineralogical Society of Great Britain and Ireland
- Date：2007-
- Format：text/html
- Language：en
- Identifier：10.1180/minmag.2007.071.5.579
- journal_abbrev：Mineralogical Magazine
- issn：0026-461X
- volume：71
- issue：5
- firstpage：579
- section：Articles
Mn-rich graftonite, (Ca,Mn<sup>2+sup>)(Fe<sup>2+sup>,Mn<sup>2+sup>)<sub>2sub>(PO<sub>4sub>)<sub>2sub>, ferrisicklerite, Li<sub>1−xsub>(Fe<sup>3+sup>,Mn<sup>2+sup>)PO<sub>4sub>, manganoan apatite, (Ca,Mn<sup>2+sup>,Fe<sup>2+sup>Mg)(PO<sub>4sub>)<sub>3sub>Cl, staněkite, Fe<sup>3+sup>Mn<sup>2+sup>O(PO<sub>4sub>) and Mn-rich vivianite, (Fe<sup>2+sup>)<sub>3sub>(PO<sub>4sub>)<sub>2sub>·8H<sub>2sub>O, occurring in a granitic pegmatite at Soè Valley (central Alps, Italy) were characterized by powder and single-crystal X-ray diffraction (XRD) and electron microprobe analyses. Geochemically, the Mn-rich graftonite phases are poorly evolved Fe/Mn-phosphates of rare-earth elements-lithium (REE-Li) granitic pegmatites. The assemblage Mn-rich graftonite + ferrisicklerite + staněkite has rarely been documented in pegmatites. In the Soè Valley pegmatite, ferrisicklerite forms exsolution lamellae with Mn-rich graftonite associated with manganoan apatite and staněkite. Graftonite is associated with Mn-rich vivianite. Powder and single-crystal XRD data indicate that the unit-cell volume of graftonite increases as a function of Mn<sup>2+sup> content. Staněkite shows a distinctly smaller unit-cell volume with respect to previously reported staněkites, probably due to reduced Mn<sup>2+sup>. Vivianite with significant Mn<sup>2+sup> has a unit-cell volume similar to nearly Mn-free vivianite. The formation of Mn-rich graftonite and manganoan apatite is related to destabilization of Mn-rich almandine and biotite during pegmatite formation. Ferrisicklerite forms exsolution lamellae along the 010 cleavage planes of Mn-rich graftonite, whereas staněkite forms by alteration of ferrisicklerite and Mn-rich vivianite due to circulation of late-stage hydrothermal fluids.