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Kenngottite, Mn (sub 2) (super 2+) Fe (sub 4) (super 3+) (PO (sub 4) ) (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 2) ; a new phosphate mineral from Krasno near Horni Slavkov, Czech Republic

Jiri Sejkora, Ian E. Grey and Anthony R. Kampf
Kenngottite, Mn (sub 2) (super 2+) Fe (sub 4) (super 3+) (PO (sub 4) ) (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 2) ; a new phosphate mineral from Krasno near Horni Slavkov, Czech Republic
European Journal of Mineralogy (May 2019) 31 (3): 629-636

Abstract

Kenngottite, Mn (sub 3) (super 2+) Fe (sub 4) (super 3+) (PO (sub 4) ) (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 2) , is a new phosphate mineral from the Krasno ore district near Horni Slavkov, Czech Republic. It occurs in association with phosphosiderite, fluorapatite, Mn-rich dufrenite, frondelite, rockbridgeite, morinite, beraunite, strengite, natrodufrenite, fluorite and a K-Mn oxide. It forms brown aggregates up to 3 mm across in tiny cavities of hydrothermally altered black rockbridgeite-group minerals. These aggregates are composed of imperfect laths to fibrous crystals up to 0.5 mm in size. Kenngottite has a light brown streak and a vitreous to pearly lustre. It does not fluoresce under either short- or long-wave ultraviolet light. Its aggregates are opaque; individual crystals or tiny fragments are translucent to transparent. Cleavage is not directly observed, probably parallel to {100}, the Mohs hardness is approximately 4-5 (by analogy with souzalite and gormanite), and the mineral is brittle with an uneven, stepped fracture. The calculated density is 3.40 g/cm (super 3) . Kenngottite is optically biaxial positive, the indices of refraction are alpha = 1.785(1), beta = 1.790(5), gamma = 1.810(2), and 2Vmeas. is 50(10) degrees . Kenngottite is monoclinic, space group P2/a, a = 13.909(10), b = 5.186(4), c = 12.159(9)Aa, beta = 98.88(1) degrees , V = 866.5(11)Aa (super 3) , Z = 2. The eight strongest lines in the X-ray powder diffraction pattern are as follows: d (alpha )/I(hkl): 4.87/47(202 (super -) ,110); 3.458/89(401 (super -) ,310); 3.209/100(203,311,113 (super -) ,013,312 (super -) ); 3.023/31(113,004); 2.623/46(114 (super -) ,204,020); 2.429/49(510,220,314 (super -) ); 1.9506/28(024,224 (super -) ) and 1.5772/34(624 (super -) ). The chemical analyses by electron microprobe yielded (in wt%) Na (sub 2) O (sub 0.03) , MnO (sub 17.82) , CaO (sub 0.31) , ZnO (sub 0.32) , Fe (sub 2) O (sub 3) 35.30, Al (sub 2) O (sub 3) 2.71, P (sub 2) O (sub 5) 30.80, As (sub 2) O (sub 5) 0.15, SiO (sub 2) 0.08, H (sub 2) O (sub calc.) 9.60, total 97.12. The resulting empirical formula on the basis of 24 O atoms per formula unit (apfu) is (Mn (sub 2.29) Fe (sub 0.53) Ca (sub 0.05) Zn (sub 0.04) Na (sub 0.01) ) (sub Sigma 2.92) (Fe (sub 3.51) Al (sub 0.49) ) (sub Sigma 4.00) [(PO (sub 4) ) (sub 3.96) (AsO (sub 4) ) (sub 0.01) (SiO (sub 4) ) (sub 0.01) ] (sub Sigma 3.98) (OH) (sub 6.42) (H (sub 2) O) (sub 1.66) . The crystal structure of kenngottite was solved using single-crystal X-ray diffraction data and refined to wR (sub obs) = 0.088 for 350 reflections with I>sigma (I). The structure contains trimeric clusters of face-shared octahedra (Mn-Fe-Mn) that are connected into chains along [001] by sharing edges with Mn-centred octahedra. The chains are corner-connected along [100] to linear corner-shared trimers of Fe-centred octahedra and along [010] via corner-connected PO (sub 4) tetrahedra. Monoclinic kenngottite is structurally related to triclinic souzalite and gormanite. It is named in honor of the prominent mineralogist Prof. Gustav Adolf Kenngott (1818-1897) from the University of Zurich (Switzerland) for his contributions to systematic mineralogy.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 31
Serial Issue: 3
Title: Kenngottite, Mn (sub 2) (super 2+) Fe (sub 4) (super 3+) (PO (sub 4) ) (sub 4) (OH) (sub 6) (H (sub 2) O) (sub 2) ; a new phosphate mineral from Krasno near Horni Slavkov, Czech Republic
Affiliation: National Museum, Department of Mineralogy and Petrology, Prague, Czech Republic
Pages: 629-636
Published: 201905
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 24
Accession Number: 2019-063923
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N50°07'22" - N50°07'22", E12°48'02" - E12°48'02"
Secondary Affiliation: Commonwealth Scientific and Industrial Research Organisation, AUS, AustraliaNatural History Museum of Los Angeles County, USA, United States
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2019
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