American Mineralogist, Volume 69, pages 380-3E2, 1984
Sinkankasite,a new phosphatefrom the Barker pegmatite, South Dakota
DoNero R. Pencon Department of Geological Sciences University of Michigan, Ann Arbor, Michigan 48109
Pere J. DUNN Department of Mineral Sciences Smithsonian Institution, Washington, D.C. 20560
Wrrrnno L. Rosenrs, THoMAs J. CnMpenrl Museam of Geology South Dakota School of Mines and Technologl Rapid City, South Dakota 57701
eNo WIlua,u B. SIuruoNs Department of Earth Sciences University of New Orleans, New Orleans, Louisiana 70148
Abstract
Sinkankasite, ideally HzMnAl(POa)z(OH). 6HzO, is a new mineral occurring as an alteration product of triphylite at the Barker pegmatite, Keystone, South Dakota. It is triclinic, spacegroup PT or Pl, with cell parametersa = 9.58(4), b :9.79(5), c : 6.88(4)4, a : 108.1(2),p: gg.6(3),y:98.7(3)',V : 590Q)A3,andZ= 2. Crvstalsare elongated on [fi)l], flattened on {100} and twinned on {100}. Sinkankasiteis transparent, colorless, has hardness4 and a good {100} cleavage.The observed and calculated densities are 2.27 and 2.25 glcm3,respectively. Optical parametersinclude: biaxial negative;2V (calc.) = 84o;a = l.5ll(2),F:1.529(2),y:1.544(2);dispersionrlv;cAY-ll".The_strongestlinesinthe powderdiffractionpatternare(d,IlIo,hk[):9.2,100, lfi); 5.41,50,111;5.06,60, lll;4.58, 40,zffi, lll;2.834, 40, 230;2.701,40, 130.The nameis in honor of Dr. John Sinkankas.
Introduction approvedprior to publication by the Commissionon New Names' IMA' The mineral describedherein was first found in 1963by Minerals and Mineral WLR and examined as part of a study of the minerals of Crystallography the Barker pegmatite (formerly known as the Ferguson pegmatite), which is located east of Keystone, South Single crystals of sinkankasitewere studied using pre- Dakota. Preliminary examinationindicated that it was not cession and Weissenbergsingle-crystal diffraction meth- a known species.Our subsequentinvestigation has con- ods. The photogqphs showed that sinkankasiteis triclin- firmed that preliminary finding, and shown it to be a new ic, spacegroup Pl or Pl, with a : 9.5E(4),b : 9.79(5),c hydratedmanganesealuminumphosphatewhichisappar-:6.88(4)A, a = 108.1(2),F=99.6(3),1:98.7(3)',andV ently unrelated to other known phases. : 590(7)A3.All crystals studied are twinned by reflection We take pleasure in naming this new mineral in honor on {100}.Powder diffraction data, listed in Table l, were of Dr. John Sinkankas, in recognition of his numerous obtained using a polycrystalline sample in a 114.6 mm contributions to mineralogy, in particular the many books diameter Gandolfi camera, CuK" radiation and Si as an he has authored and his many diverse efforts on behalfof internal standard. The Iattice parameters listed above the education of amateur mineralogists. The holotype were obtained by least-squares refinement of powder specimen is preserved in the Smithsonian Institution difraction data. under catalog #149597. The mineral and the name were Sinkankasite crystals are less than 2-3 mm in length 0003-004)v84l0304-0380$02.00 3E0 PEACOR ET AL,: SINKANKASITE 381
Table l. X-ray powder diffraction data for sinkankasite Chemistry Sinkankasite was chemically analyzed using an ARL- I/Io* d (Calc ) hkl I/lo d(obs) serraqelectron microprobe with an operating voltage of 15 100 9.2 9.22 100 30 2.428 10 1T0 2.355 kV and a sample culrent of 0.025 pA, standardizedon l0 5.86 5.86 110 10 50 5.41 5.42 117 2.2L8 brass. The data were corrected using Bence-Albee fac- 60 5.06 5.05 1n 20 2.117 tors. The standardsused were montgomeryitefor Al, Ca, 40 4.s8 4.61 200 10 1.968 Mg, P; manganite for Mn; fluorapatite for F and horn- 4.58 lTT 2 1.884 20 4.13 4.14 LzL IO 1.839 blende for Fe. A microprobe wavelength-dispersivescan 3.97 3.96 LzI L.782 1.755 indicated the absenceof any elementswith atomic num- l0 3.81 3.79 210 3.78 zTt 1.715 ber greater than 8, except those reported herein. A 20 3.24 3.25 t02 r.665 spectrographic analysis indicated the absence of light 20 3.06 3.07 300 1.607 3.07 Lzz 1.566 elements.The resultantanalysis yielded: Al2O3 13.6, FeO 3.05 307 1.548 7.5, MgO 0.2, MnO 12.2,P2Os 39.5, F 2.2 percent,with 30 2.943 1.521 : 40 2.834 1.411 water 3l.3Vo by Penfield method (total weight Vo 40 2.701 1.397 2.534 106.5%).Because the water determinationsindicated that 2 2.477 10.93%of the water was very loosely bound and lost at ll0oC, we presumed that the very high sum of the rlntensities visual ly estinated. analysisgiven above was due to volatilization of H2O in the beam of the microprobe, as is common in highly hydrated minerals with loosely bound H2O. In addition, calculatedunit cell contents were approximately lOTotoo loss water in microprobe and elongateon [fi)l], tabular on {100} and composed of high, supporting such a of the determined the forms {100},{010}, and {001},listed in order of size analysis with concomitant increases in development.Indices were determinedfrom optical goni- weight percent oxides. Accordingly, we normalized the ometer measurementsmade on a crystal oriented using weight percent oxides to sum (with 313% water) to single-crystal X-ray diffraction techniques. Sinkankasite 1008%.The normalizedanalysis is: Al2O312.6,FeO 6.9, = crystals exhibit parallel growth and a representativecrys- MgO0.2, MnO 11.3,P2O5 36.5, F 2.0,H2O 31.3, Sum : = tal cluster is shown in Figure 1. 100.8%,less0.8% O F, total 100.0percent. Cal- culation of unit cell contents yields: Ha oo(MnrzsFeo.tt Physical and optical properties Mgo.o+)>zroAlr.se eO4)4.1s(OHo.e7Fo s5)>r.72 ' ll.l3HzO' or ' Sinkankasiteis colorless.The Mohs' hardnessis ap- ideally, HzMnAl(POrh(OH) 6H2O with Z: 2. Sinkan- HCl. proximately 4 or slightly less. The density, determinedon kasiteis readily solublein dilute 1:1 Paul B. Moore, we were several crystals of the holotype using heavy liquid tech- Through the courtesy of Dr. provided wet-chemical sinkan- niques, is 2.27 glcm3,compared with the calculatedvalue subsequently a analysisof of 2.25g/cm3. There is one perfectcleavage, {100}, which is developed only with difrculty. Sinkankasite crystals part easily along {100}twin boundariesand this efect can, in multiply-twinned crystals, resemblecleavage. Crushed fragments viewed at high power commonly show two or three apparent cleavages at right angles. In addition, crystalshave a marked tendency to break at approximate- ly right angles to [fi)l], but careful examination of this feature in broken crystals by scanningelectron microsco- py failed to reveal evidence of true cleavage.In addition, this apparent plane is not precisely parallel to {001}. Sinkankasite has a vitreous luster on cleavage surfaces and a vitreous to dull luster on crystal faces, many of which are encrustedwith an unidentified mineral (Fig. l). Sinkankasite is very brittle. There is no discernible re- sponseto ultraviolet radiation. Optically, sinkankasiteis biaxial negative,with indices of refractiona: l.5ll,9:1.529, and 7: 1.544(alI -10.002).It has 2V (calc.) = 84'; dispersion r < v, moderate; c A Y - 11". Optical determinations were Fig. l. SEM photomicrograph of a cluster of sinkankasite complicated by the multiple twinning which seemsto be crystals exhibiting parallel growth and typical habit. Scalebar is intrinsic to this mineral. 100g.m. Druse coating is of an unknown mineral. PEACOR ET AL.: SINKANKASITE
kasite which had been carried out by the late Dr. Jun lto. pink to brown transluscent 3 mm crystals. Carbonate- This analysisgave MnO 12.5,FeO 7.4, MgO 0.25, ZnO apatite is younger than vivianite and hureaulite; in the 0.03,CaO 3.31, Na2O 0.(D, Al2O3 9.35, P2O5 35.30, H2O+ vugs it forms white crusts and delicate boxworks and is 14.6, H2O- 16.7, sum = 99.53 percent. Ito's spectro- composedof colorless,prismatic, bipyramidal crystals up graphic analysesshowed minor amounts of Si, Pb, Ti, Be to 0.5 mm in length. Spherulitic aggregatesand I mm and Li, the latter measured at 0.003 weight percent. crystals of pink strengite are scattered randomly on the Calculation of a chemical formula for this sinkankasiteon carbonate apatite followed by, if not contemporaneous the basis of P = 2, yields: H2(Mns.TlFes.lsMgo.ozCao.zlwith, barbosalite in very dark greenish-blue 0.5 mm Nao.or):r. rr (Alo.zrFd.ld> r.oo@o4)2 (oH) r.26 . 6.35H2O,or spherules.Fluellite, which is rather uncommon, appears ideally, H2MnA(PO4)z(OH).6H2O. This sampleis also to have formed with barbosalite and is found as clusters from the Barker pegmatiteand is quite similar in composi- of colorless, dipyramidal, I mm diameter crystals, which tion to our sample except that it contains some calcium. have large i0l0) faces. Sinkankasite, which is rather Sinkankasitehas also been found at the Palermo peg- common, is the last mineral in this sequenceand is found matite in North Groton, New Hampshire. The only as colorless, bladed, prismatic crystals up to 4 mm in known specimenhad been in the mineral collection of the length. It often occurs as divergent, radial clusters and as late Gunnar Bjareby and was provided to us by Dr. Paul spheroidalaggregates. Several specimens,which contain B. Moore. Analysis of this material, which has a powder only hureaulite and sinkankasite, have spherulesof sin- pattern indistinguishablefrom that of the type sinkanka- kankasitewithin hureaulite, indicating that in these speci- site, yields the chemical formula, on the basis of P : 2: mens, sinkankasiteformed just after the onset of hureau- Hz(Ml|orizFe6j+Mgo.os)>r.orAlo.%eo4)2(O H)o.ez. 5.47 H2O, lite crystallization, and was contemporaneouswith it. in good agreementwith that of the type material. Other secondaryphosphates found at the Barker pegma- tite, but not associated with sinkankasite, are: laueite, Occurrence and paragenesis torbernite, autunite, and phosphuranylite. Sinkankasiteis found in the Barker pegmatite, located Sinkankasite has been found at the Palermo Mine, in in the SW%, NE/n, sec 14, T2S, R6E, three miles North Groton, New Hampshire, on only one specimen.It southeastof Keystone, PenningtonCounty, South Dako- occurs as flattened, circular, 2-3 mm sprays of white ta. The primary mineralogy of the pegmatite is rather acicular crystals associatedwith vivianite in a fracture in simple. The geology has been described in detail by massive triphylite. This material was previously de- Norton (1964). scribed as gatumbaite by Segeleret al. (1981). Sinkankasite occurs as complete pseudomorphsafter Acknowledgments subhedral to euhedral triphylite and as cavity fillings formed from the partial or complete dissolution of triphy- We expressour gratitudeto Mrs. BeatriceBarker for permis- lite. These pseudomorphsand cavity replacementsrange sion to collectat the mine. We thank Lee Campbelland Jean in size from