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Secondary Zn-bearing phosphate minerals associated with alteration of phosphophyllite at Hagendorf-Sud, Bavaria

Ian E. Grey, Erich Keck, Colin M. MacRae, A. Matt Glenn, W. Gus Mumme, Anthony R. Kampf and John R. Cashion
Secondary Zn-bearing phosphate minerals associated with alteration of phosphophyllite at Hagendorf-Sud, Bavaria
European Journal of Mineralogy (May 2018) 30 (5): 1007-1020

Abstract

At the Hagendorf-Sud pegmatite, Bavaria, phosphophyllite plays an important paragenetic role in the formation of numerous Zn-bearing secondary phosphate minerals. We report the results of studies conducted on the alteration of phosphophyllite in a heavily corroded triphylite nodule from the 67 m level of the pegmatite mine. The most abundant secondary phosphate minerals associated with phosphophyllite are oxidized schoonerite-group minerals, including the new mineral schmidite, (super [5]) Zn (super [6]) ((Fe (sub 0.5) (super 3+) Mn (sub 0.5) (super 2+) ) (sub 2) ZnFe (super 3+) )(PO (sub 4) ) (sub 3) (OH) (sub 3) (H (sub 2) O ) (sub 6) .2H (sub 2) O, whose formation is contemporaneous with phosphophyllite. The phosphophyllite crystals in the nodule are characteristically covered with a composite rind of epitaxial Zn-rich jahnsite crystals on the phosphophyllite surface overlain by an orange-yellow amorphous Zn-bearing ferric phosphate and/or green mitridatite. The jahnsite crystals are compositionally zoned into two phase domains based on their Ca/Zn contents. The low-Zn domains are jahnsite-(CaMnMn) whereas the high-Zn domains correspond to a potentially new species, "jahnsite-(CaMnZn)". The amorphous phase coating the jahnsite crystals has Zn levels similar to those in jahnsite, and is probably derived from its alteration. Its properties are consistent with it being a Zn-bearing santabarbaraite. Younger idiomorphic crystals of laueite, earlshannonite and zincostrunzite occur on the phosphophyllite rind. The laueite crystals have a surface layer, approximately 5 mu m thick, in which Mn is replaced completely by a 1:1 atomic mixture of Zn + Mg, giving a composition (Zn (sub 0.5) Mg (sub 0.5) )Fe (sub 2) (super 3+) (PO (sub 4) ) (sub 2) (OH)2.8H (sub 2) O. The composition of the surface phase is explained by configurational-entropy stabilisation. The earlshannonite crystals commonly grow epitactically on the laueite, yet despite the close association, they are Zn-bearing only, with very low Mg contents. Single-crystal structure refinements have been done on both (Zn + Mg)-bearing laueite and Zn-bearing earlshannonite and all H atoms were located in both cases. Structural models are presented for the epitactic growth of jahnsite on phosphophyllite and earlshannonite on laueite.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 30
Serial Issue: 5
Title: Secondary Zn-bearing phosphate minerals associated with alteration of phosphophyllite at Hagendorf-Sud, Bavaria
Affiliation: CSIRO Mineral Resources, Clayton, Victoria, Australia
Pages: 1007-1020
Published: 20180531
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 41
Accession Number: 2018-064821
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 9 tables
N49°39'01" - N49°39'01", E12°27'34" - E12°27'34"
Secondary Affiliation: Natural History Museum of Los Angeles County, USA, United StatesMonash University, AUS, Australia
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201835
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