American Mineralogist, Volume 69, pages 920-927, l9A Hedyphanefrom Franklin, New Jerseyand Ling!,an, Sweden: cation ordering in an arsenateapatiter Rolexn C. Rouse Department of Geological Sciences University of Michigan, Ann Arbor, Michigan 46109 PBre J. DutrN Department of Mineral Sciences Smithsonian Institution, Washington, D. C. 20560 nNo DoNnr-n R. PEncon Department of Geological Sciences University of Michigan, Ann Arbor, Michigan 48109 Abstract Hedyphane, traditionally formulated as (Ca,Pb)s(AsOr,POn)rCl,is redefined as Ca2Pb3(AsOahClwith Z : 2. The spacegroup is PQlm with a = 10.140(3)and c = 7.1E5(4)4.Observed and calculateddensities are 5.E5and 5.99 g/cm3,respectively. The crystal structurehas beenrefined to residualsof 0.062(weighted) and 0.076(unweighted) using 550 reflections.Ordering of Ca and Pb on equipoints4/ and 6h, respectively,is completeexcept for a possibleminor amountof solid solution(ca. lVo).Cation ordering in hedyphaneis attributed to a preferenceby atoms with sterically active electrcinlone pairs, e.g., Pb(II), for the asymmetricallycoordinated 6ft site. A study of mineralsin the solid solution series Ca"Pb5-*(AsOa)3Clfrom Lingban, Sweden, and Franklin, New Jersey, revealsa lack of compositionsin the range2.3 s x - 4.8, implyinga miscibilitygap in this regron. Introduction lent cation sites.The A site correspondsto equipoint4/ In the course of a systematicstudy of lead calcium and is coordinatedby nine oxygen atoms at the vertices of arsenate apatites from Franklin, New Jersey, and a distorted tricapped trigonal prism, whereas the B site Ltngban, Sweden,two salient featuresappeared upon correspondsto equipoint 6/, with a coordination number tabulationof the chemical analyses.These features, a which dependson the identity of Z. That is, B is coordi- clusteringof analysesnear the ratio Pb:Ca = 3:2 and a natedby six oxygenand one Z atom when Z: F or OH conspicuouslack of compositionsin one regionalong the andby six oxygenand two Z atomswhenZ: Cl, Br, or I. Pbs(AsO+):Cl-Ca5(AsOa)3Cljoin, suggestedthat addi- (The cadmium apatitesare exceptionsto this rule (Sudar- tional study was warranted.The resultsof this investiga- sananet aI.,1977)). tion, in particular an analysis of the crystal structure of The segregationof cationsonto two nonequivalentsites hedyphane,have resulted in a redefinitionofthis mineral, creates a potential for ordering in mixed-cation apatites, which has heretofore held a rather ambiguous position the simplestpossible ordering scheme being AaBe. While within the apatite group. The data also permit some numerousapatites, both naturaland synthetic,exist with definition of the possiblelimits of solid solution in the this 4:6 ratio (Roy et al., 1978),very few have been systemPbs(AsO+)rCl-Cas(AsO+hCl. subjectedto crystal structure analysisto verify the order- The generalformula for the hexagonal(P6tlm) apatites ing implicit in their formulas. Moreover, such studies as may be written A4B6(XO4)622in recognition of the fact have been made have often relied upon powder X-ray that the structurecontains two symmetricallynonequiva- diffraction data to deduce the presenceor absenceof ordering. In this paper we present a crystal structure tContribution No. 388. The MineralogicalLaboratory, De- analysis based on single-crystaldata to demonstrate partmentof GeologicalSciences, University of Michigan. cation orderingof the 4:6 type in hedyphane. 0003-004x/84/09I 0-0920$02. 00 920 ROUSE ET AL.: HEDYPHANE 92r Nomenclature barite, barylite, rhodonite, and numerousother phases. relatively few Llngban samples,we can- Hedyphane was originally described from the type Having studied than this simple paragenetic generaliza- locality, Lingban, Sweden,by Breithaupt(1830). It also not make more of a massive,fine- occursat the Harstig Mine, Pajsberg,Sweden (Igelstrcim, tion. The neotype specimenconsists grained, rock, which is coatedwith I cm lE65;Sj<igren, 1892) and was moderatelyabundant at the calcite-bearing Theseare, in turn, coatedwith Franklin Mine, Franklin, SussexCounty, New Jersey, euhedralcalcite crystals. which euhedralindividuals from which it was described by Foshag and Gage (1925), hedyphanecrystals, occur as intergrown crystals. The Palacheand Berman (1927),and Palache(1935). Foshag and as clusters of randomly sparseamounts of allactite and and Gageproposed that hedyphanebe definedas material hedyphaneis followed by generations with Ca > Pb, leading to the formula (Ca,Pb)s(AsO+, two of hausmannite. hedyphaneoccurs in a wide variety of PO4)3C1,which is the one given in most modernmineral- At Franklin, non-silicatelead ogical compendia. However, our electron microprobe assemblagesand is the most abundant both in terms of volume and survey of a large number of specimensfrom Franklin and mineral at this deposit, the representative Lingban, some analysesof which are presentedherein, frequency of occurrence. Among Franklin hedyphane are (a) As hasfailed to produceany lead-bearingspecimens which modes of occurrence of yellow greasy-lusteredmaterial conform to the criterion of Foshagand Gage.This calls massive, to colorless, and curved, platey, into question the chemical analysispublished by these associatedwith barylite, copper, massive (b) As colorless,yellow, or gray tabular authors,who, in fact, noted that some of their material calcite. barite, and man- appearedto be slightly altered.Unfortunately, we were dipyramidsassociated with rhodonite, ganaxinite. these euhedralcrystals unable to locate the specimenthey studied and thus it The morphology of (1927) could not be reanalyzed. was describedby Palacheand Berman and Palache (1935).(c) As yellow-to-brown-to-graymassive materi- The Ca > Pb criterion of Foshagand Gagecreates a a in willemite-franklinite ore and dilemma when one tries to formally define hedyphane. al, filling fracture seams with rhodonite. (d) As stout, pris- Although these authors proposed that hedyphane be frequentlyassociated x 6 mm in size, associated consideredthe namefor materialwith Ca > Pb, they were matic, colorlesscrystals, 6 with green willemite, bright pink rhodonite, and discussingtheir own material and not other, previously bright The last-namedassemblage describedhedyphanes, all of which contain substantial copper, all in a calcite matrix. and coats a pre-existing,strongly amountsof lead and whose Pb: Ca molar ratios approxi- is clearly secondary undeterminedcomposition. mate3:2. We thereforepropose that the namehedyphane fluorescentapatite of be restrictedto material which meets the following re- quirements:that Pb and Ca be major elementshaving a Physical description -3:2, molarratio of that As exceedP, and that Cl exceed The neotypehedyphane occurs as light yellow, euhe- F or (OH). Defined in this way, the ideal formula of dral crystals approximately I mm in maximum dimen- hedyphanebecomes Ca2Pb3(AsOahCl. previ- The niche sion. They are tabular on {0001},and the form develop- ously assignedto this mineral,namely (Ca,Pb)5(AsOa)3Cl ment is similar to that figured by Palache and Berman with Ca > Pb, or ideally the end-memberCa5(AsOa)3CI, (1927). The morphologies of the Swedish and Franklin is now vacant. Material with this ideal end-member crystals are similar. Hedyphane is translucent with a compositionhas been discovered,however, and is now white streakand hasa greasyto vitreousluster on crystal beingcharacterized. When this is accomplished,it will fill faces and fracture surfaces. The Mohs hardness is ap- the niche previously assignedto hedyphaneby Foshag proximately4. Cleavageis indiscernible,the fracture is and Cage.This nomenclaturalscheme is advantageousin even, and the mineral is moderately brittle. Density that it retainsthe namehedyphane for thosecompositions measurementsmade with a Bermanbalance gave values previouslydescribed as hedyphanein the literature,thus rangingfrom 5.71 to 5.85 g/cm3. with the latter value ensuringcontinuity. This redefinitionof hedyphanewas closest to that calculated from the ideal formula, namely proposedto the IMA Commissionon New Minerals and 5.99 glcm3. Optically, neotype hedyphane is uniaxial Mineral Names as part of a submissionon turneaureite positivewith a meanindex of refractionbetween l 95 and and has been approvedby that body. 1.965.The observation is in agreementwith those of We have chosenfor the neotypehedyphane the Har- Palache and Berman (1927), who found Franklin hedy- vard University specimenH-90411 , from Lflngban,Swe- phaneto have indices e = 1.958and ar = 1.948. den. Material from this specimenhas been used in a Although the arsenateapatites from Franklin cannot, in determinationof the crystalstructure and for the determi- general,be unambiguouslyidentified on the basisof their nation of the chemical,unit cell, and spacegroup data variedresponses to ultravioletradiation, the lead-bearing presentedherein. members(mimetite and hedyphane)have a very weak, Occurrence light yellow fluorescence.Johnbaumite, Cas(AsO+)rOH, Hedyphaneoccurs at Lingban both in massiveform showsa strongorange fluorescence, which is characteris- and as euhedralcrystals. It is frequentlyassociated with tic of this mineral. 922 ROUSE ET AL.: HEDYPHANE Chemistry and X-ray crystallography Table2. Electronmicroprobe analyses ofhedyphane and related speciesfrom Lingban, Sweden The sampleswere chemicallyanalyzed using an anl- seuq electron microprobe utilizing an operating voltage specimen cao BaO Pbo Pz0s As205 cl 0=cl'F Total of 15kV and a samplecurrent of 0.025g,A, measuredon brass. The standardsused were synthetic PbO (Pb), 134981 43.8 0.7