Description, crystal structure, and paragenesis of krettnichite, PbMn3

Eur J Mineral2001 13 145-158

Description crystal structureand paragenesis of krettnichite PbMn3+2(VO4)2(OH)2

the Mn3+ analogue of mounanaite

JOEumlL BRUGGER1 THOMAS ARMBRUSTER2 ALAN CRIDDLE3 PETER BERLEPSCH4STEFAN GRAESER5 and SHANE REEVES6

1VIEPS Department of Earth Sciences VIC-3800 Monash University Australia

2Laboratory of Chemical and Mineralogical Crystallography University of BernFreiestrasse 3 3012 Bern Switzerland

3Department of Mineralogy The Natural History MuseumCromwell Road SW7 5BD London UK

4Institute of Geology University of Copenhagen Oslashstervoldgade 101350 Copenhagen Denmark

5Institute for Mineralogy and Petrography University of BaselBernoullistrasse 30 4056 Basel Switzerland

6VIEPS School of Earth Sciences The University of MelbourneParkville VIC 3052 Australia

Abstract Krettnichite PbMn3+2(VO4)2(OH)2 occurs as an accessory ore mineral and as free crystals in vugs with-

in the hydrothermal manganite-quartz vein at the historic manganese deposit of Krettnich Saarland Germany Othervein minerals include barite ankerite calcian mottramite (minor ore constituents) barian brackebuschite cobaltoanpyrobelonite and calcian mottramite (free crystals in vugs) Krettnichite is monoclinic space group C2m Z = 2a = 9275(7) Aring b = 6284(3) Aring c = 7682(2) Aring b = 11797(4)deg Krettnichite is brown to black with red internal reflec-tions It has an excellent cleavage parallel to (001) A distinct cleavage intersecting (001) at high angle is visible inpolished section Polysynthetic twinning with composition plane (001) is common Under plane polarised reflectedlight krettnichite is slightly pleochroic from very light grey to light brownish grey and the anisotropy is strong undercrossed polars

Krettnichite is a member of the tsumcorite group It is the second member of this group with vanadate as the dom-inant anionic group and is thus the Mn3+ analogue of mounanaite PbFe3+

2(VO4)2(OH)2 The Fe content of krettni-chite is generally low and some crystals contain less than 0001 atom Fe pfu Epitactic intergrowths of krettnichiteand brackebuschite are common with parallel alignment of the b axes of both minerals This direction correspondsto the extension of trans-trans chains of edge-sharing Jahn-Teller distorted Mn3+O6 octahedra in krettnichite as wellas in brackebuschite Pyrobelonite is always closely associated with barian brackebuschite It is not known if true epi-taxy occurs but the chains of edge-sharing Mn3+O6 octahedra of brackebuschite match edge-sharing chains ofMn2+O6 octahedra in pyrobelonite

Key-words krettnichite brackebuschite mottramite pyrobelonite crystal structure Jahn-Teller distortion man-ganese deposit

0935-1221010013-0145 $ 350atilde 2001 E Schweizerbartrsquosche Verlagsbuchhandlung D-70176 Stuttgart

E-mail joelbmailearthmonasheduau

DOI 1011270935-1221010013-0145

J Brugger T Armbruster A Criddle P Berlepsch S Graeser S Reeves

Introduction

A great diversity of V and As minerals formduring the metamorphism of syngenetic Mndeposits and are important constituents of the

mineral association in some of the worldrsquos famousmineralogical localities such as Laringngban Sweden(Bostroumlm et al 1979) and Franklin New Jersey(eg Frondel amp Baum 1974) Indeed most meta-morphosed syngenetic Mn deposits of likely

146

Fig 1 (a) Scanning electron microscope image of a prismatic krettnichite (kr) aggregate associated with manganite(ma) and barian brackebuschite (br) in a vug The inset is a close-up illustrating the morphology of brackebuschiteThe orientation of the crystallographic axes was retrieved by single-crystal Weissenberg and precession camera mea-surements (b) Hand drawing of a pseudo-rhombohedral krettnichite (kr) crystal occurring in a vug with manganite(ma) and carrying epitactic brackebuschite needles (br) Drawing by Klaus Schaumlfer size of the krettnichite crystal08 mm (c) Microphotograph of a krettnichite (kr) aggregate Diameter of the rosette about 8 mm Photograph byKlaus Schaumlfer

exhalative origin contain unusual V or As miner-als and in the past few years several new miner-als have been described from little known depositsof this type (eg fianelite Brugger amp Berlepsch1996 nabiasite Brugger et al 1999)

In the present paper we describe a new Mnvanadate from a different kind of Mn deposit anon-metamorphosed hydrothermal vein The pres-ence of two unknown vanadates in the Mn veinsnear Krettnich (Saarland Germany) has been pre-viously reported by Muumlller (1984 1988) The firstmineral described as a V analogue of laquob-duftiteraquois in fact a calcian mottramite (Reiss amp Raber1998) Our investigations confirm that the secondvanadate is a new mineral that we named krettni-chite in reference to the type locality The mineraland its name have been approuved by theInternational Mineralogical Association (IMA)Type material is deposited at the Museacutee Cantonalde Geacuteologie Lausanne Switzerland (SampleMGL 65317) and the polished section from thetype specimen is hosted at the Natural HistoryMuseum London UK Krettnichite is a newmember of the tsumcorite group with general for-mula AB2(XO4)(OH)2 Among the minerals of thisgroup krettnichite PbMn3+

2(VO4)2(OH)2 is mostclosely related to mounanaite PbFe3+

2(VO4)2(OH)2

Occurrence

The studied samples were collected from themullock dumps lining the outcrop of the mangan-ite vein south of Krettnich Saarland GermanyThe Krettnich Mn deposit consists of one to twoparallel veins which can be followed over 1200 m

and which are embedded in the PermianldquoOberrotliegenden Fanglomeraterdquo (WadernerFacies) The latter formation locally contains highcarbonate contents and in those places replace-ment of host rock by Mn minerals is common nearthe veins The veins consist of manganite[g-Mn3+OOH] quartz barite ankerite with minoramounts of mottramite [(PbCa)CuVO4(OH)] andkrettnichite Most of these minerals (notably man-ganite and mottramite) occur in both collomorphicand well crystallised forms (Muumlller 1988) Barianbrackebuschite [(PbBa)2(MnFe)(VO4)2H2O] isapparently restricted to small vugs where it formsaggregates of parallel needles (Fig 1a and 2) oroccurs in epitaxy with krettnichite (Fig 1b) Thebrackebuschite crystals are elongated along [010]and flattened along [100] (Fig 1a) Sub-millimet-ric crystals of cuprian-cobaltoan pyrobelonite[Pb(Mn2+Cu2+Co2+)VO4(OH)] occur on andintergrown with brackebuschite (Fig 2)

According to Muumlller (1988) the Krettnichdeposit formed during the interaction of ascend-ing reducing metal-rich (Mn Fe Ba Cu Pb)brines with oxygen-bearing diagenetic watersfrom the porous conglomerates The Eh-pH condi-tions were such that Mn oxideshydroxides precip-itated whereas Fe remained in solution(Krauskopf 1957) The vanadates mottramite andkrettnichite crystallised with the main ore mineralsduring this hydrothermal event Mottramite occursover the whole width of the vein but krettnichiteis restricted to the central part of the vein (obser-vation by Muumlller (1988) the in situ mineralisationis not accessible any more) The origin of thevanadium is unclear but the embedding Permianrocks (red-beds) are a likely source

Most members of the tsumcorite group result

Description crystal structure and paragenesis of krettnichite 147

Fig 2 Scanning electron microscopepicture showing idiomorphic pyrobelonitecrystals (pb) growing on and intergrownwith brackebuschite (bk)


from the hypogene oxidation of ore deposits Oneexception is cabalzarite which sometimes occursin veinlets formed during the retrograde very low-grade metamorphism of a Mn deposit (Brugger etal 2000) In contrast krettnichite does not repre-sent an alteration or late remobilisation product ofa pre-existing metal concentration but is a prima-ry mineral crystallising during the last stages ofthe hydrothermal vein formation at Krettnich

Appearanceand physical properties of krettnichite

Krettnichite occurs as radiating aggregates ofdark brown platy crystals (plates to (001)) up to3 cm in diameter within massive manganite ores(Fig 1c) In cavities krettnichite forms tiny(lt 1 mm) acicular to prismatic black crystals withadamantine lustre and orange-red internal reflec-tion (Fig 1a) as well as pseudo-rhombohedralcrystals of brownish colour and tern lustre(Fig 1b) The streak is brown and no fluorescenceis observed under shortwave or longwave ultravio-let light Optical goniometer measurements on apseudo-rhombohedral single crystal revealed thepinacoid [001] and the prisms [111] [332] and[331] (Fig 3) The acicular crystals appear to beconstituted by a pinacoid [001] and a prism[hk0] however Weissenberg diffraction imagesreveal that these ldquocrystalsrdquo are complex aggre-gates and that their elongation axis [579(4) Aring]does not correspond to a main crystallographicaxis

Krettnichite sinks in Clerici liquor (D = 404 gcm3) and the densities calculated with a cell vol-ume of 3987 Aring3 for the available electron-micro-probe analyses range between 451 and 481 gcm3Microhardness measurements were made on threedifferent krettnichite aggregates in a single pol-ished section with a load of 100 pondsAggregate 1 which was cut almost perpendicularto (001) displays lower values (mean 276kgmm2 range 266-287 kgmm2 n = 5) thanaggregates 2 and 3 (mean 347 kgmm2 range 306-383 kgmm2 n = 10) which are both orientednearly parallel to (001) It is possible that the mea-sured hardness of aggregates 2 and 3 was affectedby micro-inclusions (often lt 1 microm) of a mineralwith a high reflectivity which have been observedin some areas but the difference most likelyreflects the effect of orientation All of the inden-tations had concave sides and were fractured TheVickerrsquos hardness corresponds to a Mohrsquos hard-ness of about 45 Krettnichite displays a polysyn-

thetic twinning with composition plane (001)(Fig 4) which is identical to that found inmounanaite (Krause et al 1998) Krettnichite hasan excellent cleavage along (001) and a distinctcleavage at high angle to (001) is recognised inpolished section (Fig 4b)

Optical properties of krettnichite

Only thin cleavage plates parallel (001) aretransparent The colour is reddish brown and dis-tinct pleochroism towards orange is visible in planepolarised light Under plane polarised reflectedlight krettnichite is distinctly bireflectant andslightly pleochroic from very light grey to lightbrownish grey Under crossed polars the mineralshows straight extinction The anisotropy is strongbut rotation tints are not very colourful and fromextinction the sequence is dark metallic bluelighter blue-grey silver light purplish brown-grey

148

Fig 3 Ideal drawing of the morphology of a pseudo-rhombohedral krettnichite crystal from opticalgoniometer measurements of a real crystal (2m sym-metry)

At high magnification and under oil immersionorange-red to red internal reflections appear lsquogem-likersquo within the crystals ndash they are the more notice-able where the ordinary reflected light is dark blue(along the crystal elongation) Reflectivity data forair and oil are reported in Table 1

Optical constants were calculated from thespectral reflectance data using Koenigsbergerrsquosequations (for absorbing materials) At 590 nm nfor R1 is 221 (plusmn 001) k = 01 (plusmn 003) and for R2n is 239 (plusmn 003) k = 02 (plusmn 002) Obviouslyfrom randomly cut sections it is impossible toobtain constants that correspond to the optical orcrystallographic symmetry of the mineral Thesedata are however reproducible across three differ-ent krettnichite aggregates and so are a goodguide to the extreme values for the mineral

The Gladstone-Dale relationship gives withthe constants of Mandarino (1976) values of themean refractive index between 211 and 218 forthe range of compositions determined by the elec-tron microprobe These calculated values arelower than those obtained from the reflectancemeasurements This discrepancy arises from thefact that krettnichite is light absorbing a feature


Fig 4 Reflected-light micrograph of krettnichite (a) Aggregate showing polysynthetic twinning Length of theaggregate about 3 mm crossed polars (b) and (c) close up of the crystal shown in (a) (b) with plane polarised lightand (c) with crossed polars

Table 1 Reflectivity data on krettnichite


that is not taken into account by the Gladstone-Dale model

Chemistry of krettnichite

The chemical composition of several krettni-chite aggregates from the type specimen and anadditional sample has been determined with aCAMECA SX50 electron microprobe (EMP)operated at 15 kV 25 nA Counting time was 10 s

on each peak and 5 s on each side of the peak forthe background and the beam was defocused to adiameter of about 10-15 microm The standards werepure metals for V Mn Ni Co Cu Zn galena forPb arsenopyrite for As wollastonite for Ca andSi sapphire for Al strontianite for Sr benitoite forBa rutile for Ti and hematite for Fe

With the assumption of a trivalent oxidationstate for Mn the EMP analyses lead to the simpli-fied empirical formula PbMn3+

2(VO4)2(OH)2 andemphasise the similarity between krettnichite and

150

Table 2 Electron microprobe analyses of krettnichite

mounanaite PbFe3+2(VO4)2(OH)2 (Table 2) The

prevalence of the trivalent oxidation state of Mn inkrettnichite has been confirmed by the crystalstructure refinement (bond valence sums and sitetopology see below) The analysed krettnichiteaggregates fall into two groups Fe-free(lt 005 wt Fe2O3) and Fe-bearing (gt 1 wtFe2O3 Table 2 Fig 5a) Fe3+ is the main cation onthe octahedral site (B) of mounanaite as octahe-dral Fe3+ and Mn3+ have the same ionic radius(0645 Aring Shannon 1976) one would expect Fe3+

to occur on the octahedral site of krettnichiteHowever no correlation is apparent between Feand the other metals of the octahedral site (egFig 5a) The Fe content is not the only chemicaldifference between Fe-free and Fe-bearing krettni-chite There is a distinct negative correlationbetween As and V (substitution As = V) in Fe-freekrettnichite but none in the Fe-bearing variety(Fig 5b) The best inter-element correlations inthe available data set occur in the Fe-bearing vari-ety between Pb and V (Fig 5c slope about 12)

and between Mn and V (Fig 5d slope -12) Thesefeatures are probably due to the presence of sub-microscopic Fe- and Mn-rich solid inclusions inthe analysis volume Micrometric inclusions haveindeed been observed in some areas with opticalmicroscopy

IR spectra collected on a krettnichite powderusing an infrared microscope attached to a 1760XPerkin Elmer FTIR spectrometer show a broadabsorption band centred at 3225 cm-1 (O-H stretch-ing mode) According to the bond distance-fre-quency correlation of Libowitzky (1999) thisfrequency is in excellent agreement with the O1-O1bond distance of 269 Aring found by structure analysis(see below) The OH-positions in tsumcorite-groupminerals can also host H2O groups according tothe coupled substitution [VI]Me3+(OH)- =[VI]Me2+(H2O) (Krause et al 1998) As the octa-hedral site in krettnichite is occupied by trivalentcations (Table 2) one expects low H2O contentsand the absence of indication for molecular watereither by a bending mode around 1650 cm-1 or by


Fig 5 Diagrams illustrating the chemical variability of krettnichite (a) Composition of the octahedral site(Mn+Al+Ni+Co+Cu+Zn) vs Fe (b) Composition of the tetrahedral site As vs V (c) Correlation between Pb and V(d) Correlation between Mn and V The correlation lines and corresponding equations in (c) and (d) are for the Fe-bearing krettnichite in MGL65317


a combination mode of bending and stretchingfundamental around 5000-5200 cm-1 confirmsthis assumption It is worth mentioning that the IRspectrum obtained on untreated krettnichite is verydifferent from that obtained using KBr pellets Thelatter display two absorption bands at 3440 and3110 cm-1 as well as a clear water bending modeband at 1637 cm-1 This indicates that krettnichitedecomposes in the KBr pellet as a result of thehigh pressure andor of chemical reaction with theKBr

Crystal chemistryof the associated minerals

Manganite associated with krettnichite in vugshosts significant amounts of transition metals(010 wt NiO 014 wt CoO 039 wt CuO014 wt ZnO) and Al2O3 (145 wt mean of 6EMP analyses)

Brackebuschite from Krettnich is charac-terised by relatively high Ba contents rangingfrom 148 up to 1142 wt BaO the highest value

corresponding to 049 Ba on the Pb site (Fig 6a)The substitution of Ba for Pb is confirmed by anegative correlation with a slope close to -1 in aBa vs Pb diagram (Fig 6a) Brackebuschite fromthe type locality (Venus Mine Argentina) isBa-poor ( sup2 001 Ba pfu Foley et al 1997) butBa-dominant phases with the brackebuschitestructure are known (eg gamagariteBa2(Fe3+Mn3+)(VO4)2 (OH)) Limited substitu-tion of Mn by Fe Al Co and Cu (lt 30 ) alsooccurs (Fig 6b Table 3)

152

Fig 6 Chemical variability of the brackebuschite fromKrettnich (a) Ba vs Pb diagram (b) (Fe+Al+Co+Cu)vs Mn diagram

Table 3 Electron microprobe analyses of brackebus-chite cuprian and cobaltian pyrobelonite and calcianmottramite associated with krettnichite

The general formula of the minerals of thedescloizite group is AB2+(XO4)(OH) At Krettnichdescloizite group minerals have Pb dominating onthe A site and V dominating on the X site On theB site both Cu2+ (mottramite) and Mn2+ (pyro-belonite) have been found to dominate Indeedthree chemical types can be distinguished amongdescloizite group minerals at Krettnich (Fig 7a)(1) Ca-rich mottramite with gt 80 mol Cu on theB site and CaPb ratios up to ~ 05 (2) Ca-poormottramite with gt 40 mol Cu on B andCaPb lt 015 (3) pyrobelonite with 10 to30 mol Co and 15 to 50 mol Cu on B and verylow Ca contents One isolated analysis only plotsin the Co field of the Mn-Cu-Co triangle (Fig 7a)

Pyrobelonite mostly occurs as small idiomorphiccrystals in close association with brackebuschite(Fig 2) Pyrobelonite is devoid of As but mot-tramite shows significant As2O5 contents up to289 wt (Fig 7b)

Mottramite PbCu(VO4)(OH) Pnma is struc-turally closely related to duftite PbCu(AsO4)(OH) P212121 Kharisun et al (1998) showed thatldquob-duftiterdquo an intermediate member betweenduftite and conichalcite CaCu(AsO4)(OH)P212121 was characterised by domains about 50 Aringin size where the Jahn-Teller distorted CuO6 octa-hedra are oriented differently The Ca analogue ofmottramite is tangeite CaCu(VO4)(OH) withspace group P212121 and therefore a symmetry


Fig 7 Chemical variability of the mot-tramite and pyrobelonite fromKrettnich (a) Three-dimensional plotillustrating the composition of the A(PbCa) and B (CuMnCo) sites (b) Mnvs As diagram


transition must occur somewhere along the seriesbetween mottramite and tangeite The mottramitefrom Krettnich is Ca-rich (up to ~ 05 Ca pfuFig 7a) but does not show evidence for a devia-tion from the Pnma space group (Reiss amp Raber1998 and pers comm)

X-ray crystallography of krettnichite

The X-ray powder pattern of krettnichite is

reported in Table 4 The unit-cell refined fromthese data is compared to that obtained from thesingle-crystal diffractometer data and to that ofmounanaite in Table 5 The agreement is excellentgiven the chemical variability of krettnichite

Single-crystal X-ray intensity data were col-lected for a platy crystal (002 x 015 x 020 mm)on a Siemens three-circle SMART system usingMoKa X-radiation (Table 6) Structure solutionand refinement was carried out with the SHELX-97 program package (Sheldrick 1997) applying

154

Table 4 X-ray powder data for krettnichite

neutral-atom scattering factors Prior to structuresolution by direct methods the isotypic relation-ship with mounanaite was not recognised Anempirical absorption correction was carried outwith a psi-scan related method where redundantand symmetry-equivalent reflections in the variousframes were compared to calculate transmissionfactors Test refinements were performed in spacegroups C2 Cm and C2m Subsequent examina-tion of the results indicated that C2m symmetrywas correct The scattering power on the eight-coordinated Pb site indicated a mixed occupancyof dominant Pb and lighter elements (Ca and Sr)Thus the populations of Pb and Sr were allowed tovary Final difference Fourier maps revealed max-imum peaks of plusmn 2 eAring3 located around Pb and VDue to the strong scattering power of Pb localisa-tion of H sites was not attempted Atomic coordi-nates and anisotropic displacement parameters aregiven in Table 7 interatomic distances and bond-valence sums in Table 8

Crystal structure of krettnichiteand relations to other minerals

Krettnichite is isostructural with tsumcorite(Tillmanns amp Gebert 1973 Krause et al 1998)The only other member of the tsumcorite group

with dominant V is mounanaite (Cesbron ampFritsche 1969 structure refinement in Krause etal 1998) and krettnichite can be described as afairly pure Mn3+ analogue of mounanaite withMnmiddot (MnFeAlNiCoCu Zn) = 076-089 AfterMn3+ the most abundant cation on the octahedralsite is Co (Comiddot (VI) up to 016 Table 2)


Table 5 Unit cells determined for krettnichite Table 6 Parameters for crystal structure determinationand refinement

Table 7 Final atomic positional parameters Ueq (x 102) and anisotropic displacement parameters Uij (x 102) forkrettnichte Standard deviations in parentheses


Mn is one of the few elements that occur com-monly with three different oxidation states innature (Mn2+ Mn3+ Mn4+) The trivalent state ofMn in krettnichite which has been suggested byanalogy to the trivalent state of Fe in mounanaiteis confirmed by bond valence calculations(Table 8) and also by the characteristics of thecoordination polyhedron around Mn Krettnichitedisplays a dilatation of the B-O2 bond relative toB-O1 and B-O3 (Table 8) Such a distortion is notobserved in the B-octahedron in mounanaite

occupied by Fe3+ and is attributable to the Jahn-Teller effect on the Mn3+ ([Ar] 3d4) ion in high-spin state (t2g3eg1) Foley et al (1997) list 30oxygen-bearing minerals with Mn3+ as a mainconstituent In all but one case (laringngbanite) Mn3+

occurs in distorted octahedral coordination withoxygen Most Mn3+ minerals display an elonga-tion of an axis of the Mn3+O6 octahedron similar towhat is observed in krettnichite indicating that thelone electron occupies the dz2 orbital and not thedx2-y2 orbital

156

Table 8 Interatomic distances (Aring) and bond-valence sums (v) for krettnichite and mounanaite

Line-4 read ldquoMean Svrdquo instead of ldquoMean h vrdquo

Fig 8 Structural relations between krettnichite (ab) brackebuschite (c) and pyrobelonite (d) Only one layer of Mnchains is shown the next layer is obtained by a translation for krettnichite and brackebuschite and by a reflectionand a translation for pyrobelonite

Krettnichite is the third known natural Pb-Mn-(hydroxy)-vanadate and the second in which Mnoccurs as a trivalent cationBrackebuschite Pb2(Mn3+Fe3+)(VO4)2(OH)

(Foley et al 1997)Pyrobelonite Pb Mn2+ VO4 (OH)

(Donaldson amp Barnes 1955)All three known natural Pb-Mn-(hydroxy)-

vanadates occur in close association at KrettnichAn interesting feature of Mn3+ in minerals is thepredominance of octahedral chains decorated bytetrahedra (Foley et al 1997) These chains dis-play different arrangements depending upon therelative orientation of the Jahn-Teller distortion(Hoffmann et al 1997) Brackebuschite and kret-tnichite contain trans-trans-chains of edge-sharingdistorted Mn3+O6 octahedra extending along the b-axis In krettnichite the octahedral chains arelinked by VO4 tetrahedra (Fig 8a) In brackebus-chite the octahedral chains are decorated in a sim-ilar way by VO4 tetrahedra but in this case thechains are isolated (Fig 8c) Epitaxial inter-growths of krettnichite and brackebuschite arecommon with the b-axis of brackebuschite paral-lel to the b-axis of krettnichite (Fig 1b and 3) Theb-axis is the direction of the octahedral chains inboth krettnichite and brackebuschite (Fig 8a and8c respectively) Therefore we propose that theepitaxy develops between the (201) plane of kret-tnichite and the (102) plane of brackebuschitewhich contain very similar atomic arrangements(Fig 8bc)

Another interesting association occursbetween brackebuschite and pyrobelonite atKrettnich Some samples contain both pyro-belonite which grows directly on brackebuschiteand isolated crystals of mottramite Apparentlyboth minerals grew under similar conditions per-haps even at the same time and the chemical dif-ference is likely to be related to themicro-environment The elevated Mn and Co con-tents and the low As contents of pyrobelonitecompared to mottramite may be linked to the con-tents of these elements in brackebuschite Theatomic arrangement of pyrobelonite in the (001)plane is very similar to that of brackebuschite inthe (102) plane (Fig 8cd) despite the fact that theoctahedral chains contain Mn2+ and Mn3+ respec-tively The close association between brackebus-chite and pyrobelonite may result from the closestructural relationship between both phases(Fig 8cd) although it is not known whether trueepitactic growth occurs

Acknowledgements We are grateful to Hartmut

Hensel (NeustadtWeinstraszlige) for bringing thevanadates from Krettnich to our attention and forgenerously providing some of his best samples forinvestigation Indeed this work relies on manydays of prospecting and binocular examination byHartmut Hensel Klaus Schaumlfer (Idar Oberstein)and Thomas Raber (NeunkirchenSaar) andwould not have been possible without the enthusi-asm of these collectors for scientific mineralogyWe are grateful to Alexander Priymak (MelbourneUniversity) for helping with the EMP analysesand to Richard Guggenheim and his team at theREM-Labor (University of Basel) for the SEMimage in Fig 2 The paper greatly benefited fromthe comments of Jefrey A Foley (MiamiUniversity) Herta Effenberger and Uwe Kolitsch(Geozentrum Wien) and Eugen Libowitzky(Geozentrum Wien) who also measured the IR-spectrum of krettnichite and helped with its inter-pretation

References

Bostroumlm K Rydell H Joensuu O (1979) Laringgban ndashan exhalative sedimentary deposit Econ Geol 741002-1011

Brese NE amp OrsquoKeeffe M (1991) Bond-valenceparameters for solids Acta Cryst B47 192-197

Brugger J amp Berlepsch P (1996) Description andcrystal structure of fianelite Mn2V(VAs)O72H2O anew mineral from Fianel Val Ferrera (GraubuumlndenSwitzerland) Am Mineral 81 1270-1276

Brugger J Bonin M Meisser N Schenk KBerlepsch P Ragu A (1999) Description andcrystal structure of nabiasite BaMn9(VO4)6(OH)2 anew mineral from Central Pyreacuteneacutees (France) Eur JMineral 11 879-890

Brugger J Meisser N Schenk K Berlepsch PBonin M Armbruster T Nyfeler D Schmidt S(2000) Description and crystal structure ofcabalzarite Ca(MgAlFe)2(AsO4)2(H2OOH)2 anew mineral of the tsumcorite group Am Mineral85 1307-1314

Cesbron F amp Fritsche J (1969) La mounanaite unnouveau vanadate de fer et de plomb hydrateacute BullSoc fr Mineacuteral Cristallogr 92 196-202

Donaldson DM amp Barnes WH (1955) The structuresof the minerals of the descloizite and adelite groupsII-pyrobelonite Am Mineral 40 580-596

Foley J Hughes JM Lange D (1997) The atomicarrangement of brackebuschite redefined asPb2(Mn3+Fe3+)(VO4)2(OH) and comments onMn3+ octahedra Can Mineral 35 1027-1033

Frondel C amp Baum JL (1974) Structure and mineral-ogy of the Franklin zinc-iron-manganese depositNew Jersey Econ Geol 69 157-180



Hoffmann C Armbruster T Kunz M (1997)Structure refinement of (001) disordered gaude-froyite Ca4Mn3+

3[(BO3)3(CO3)O3] Jahn-Teller-dis-tortion in edge-sharing chains of Mn3+O6 octahedraEur J Mineral 9 7-19

Holland TJB amp Redfern SAT (1997) Unit cellrefinement from powder diffraction data the use ofregression diagnostics Mineral Mag 61 65-77

Kharisun Taylor MR Bevan DJM Pring A(1998) The crystal chemistry of duftitePbCuAsO4(OH) and the b-duftite problem MineralMag 62 121-130

Krause W Belendorff K Bernhardt H-JMcCammon C Effenberger H Mikenda W(1998) Crystal chemistry of the tsumcorite-groupminerals New data on ferrilotharmeyerite tsum-corite thometzekite mounanaite helmutwinkleriteand a redefinition of gartrellite Eur J Mineral 10179-206

Krauskopf KB (1957) Separation of Mn from Fe insedimentary processes Geochim Cosmochim Acta12 61-84

Libowitzky E (1999) Correlation of O-H stretchingfrequencies and O-HO hydrogen bond lengths inminerals Monatshefte fuumlr Chemie 130 1047-1059

Mandarino JA (1976) The Gladstone-Dale relation-ship Part I derivation of new constants CanMineral 14 498-502

Muumlller G (1984) Duftite von Krettnich (N-Saarland) -eine Fehlbestimmung Aufschluss 35 273-278

mdash (1988) Gedanken zu den Mineralisationen imSaarland und in seiner Umgebung Aufschluss 39257-268

Reiss GJ amp Raber T (1998) Mottramit aus Krettnich(Saarland) Lapis 23 11 39

Shannon RD (1976) Revised effective ionic radii andsystematic studies of interatomic distances inhalides and chalcogenides Acta Cryst A32 751-767

Sheldrick GM (1997) SHELX-97 program for crystalstructure determination University of GoumlttingenGermany

Tillmanns E amp Gebert W (1973) The crystal structureof tsumcorite a new mineral from the TsumebMine SW Africa Acta Cryst B29 2789-2794

Received 10 November 1999Modified version received 26 June 2000Accepted 21 July 2000

158


Introduction

A great diversity of V and As minerals formduring the metamorphism of syngenetic Mndeposits and are important constituents of the

mineral association in some of the worldrsquos famousmineralogical localities such as Laringngban Sweden(Bostroumlm et al 1979) and Franklin New Jersey(eg Frondel amp Baum 1974) Indeed most meta-morphosed syngenetic Mn deposits of likely

146

Fig 1 (a) Scanning electron microscope image of a prismatic krettnichite (kr) aggregate associated with manganite(ma) and barian brackebuschite (br) in a vug The inset is a close-up illustrating the morphology of brackebuschiteThe orientation of the crystallographic axes was retrieved by single-crystal Weissenberg and precession camera mea-surements (b) Hand drawing of a pseudo-rhombohedral krettnichite (kr) crystal occurring in a vug with manganite(ma) and carrying epitactic brackebuschite needles (br) Drawing by Klaus Schaumlfer size of the krettnichite crystal08 mm (c) Microphotograph of a krettnichite (kr) aggregate Diameter of the rosette about 8 mm Photograph byKlaus Schaumlfer




2(VO4)2(OH)2

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Description, crystal structure, and paragenesis of krettnichite, PbMn3

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