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Home , Ashburtonite, Bayldonite, Beudantite, Brochantite, Caledonite, Chlorargyrite

American Mineralogist, Volume 76, pages 1701-1707, 1991

Ashburtonite, a new bicarbonate-silicatemineral from Ashburton Downs, Western Australia: Description and structure determination

Jorr, D. Gnrcn SciencesSection, Canadian Museum of Nature. Ottawa. Ontario KIP 6P4, Canada Enxnsr H. Nrcxnr, Division of Mineral Products, CSIRO, Wembley, Westem Australia 6014, Australia Rorrnr A. Gaur.r Mineral SciencesSection, Canadian Museum of Nature, Ottawa. Ontario KIP 6P4, Canada

Ansrnlcr , ideally HPboCuoSioOrr(HCO3)4(OH)oCl,is a new mineral from Ashburton Downs, Western Australia. It occurs as clustersof clear blue, prismatic crystals up to 0.4 mm long. Associated include , , , , platt- nerite, ,, and . The mineral has a vitreous luster and light blue . It is brittle with a conchoidal . Ashburtonite is uniaxial positive with ar: 1.786(3)and e : 1.800(4).It is tetragonal,space group l4/m, with a : 14.234(7),c : 6.103(5)A, and Z:2. The strongestX-ray powder-diffractionlines areld(A), I, hk\ 10.2(100,1l0),5.644(70,101), 4.495(100,310), 3.333(100,321), 3.013(90,41l), 2.805(30,202),2.611(50,222), 2.010(30,710,103,631), 1.656(30,642,503). Crystals are elongatedon [001] with forms {ll0}, {100}, {001}, and {301}. The infraredspectrum indicates the presenceof OH and CO, groups.An electron-microprobeanalysis gave PbO 52.2,CuO 18.7,SiO, 14.1,Cl 2.3,HrO(calc.)4.22 and COr(calc.)10.31, -O = Cl: 0.51, total 101.20wto/o; D*,": 4.69 g/cm3.The structurehas beenrefined to R : 3.5 and R* : 2.4o/o.The four-membered, tetrahedral silicate rings are cross linked by ribbons of edge-sharedCu octahedra. The [HCO,] groups are loosely bonded to the sides of larye c axis channels by Cu octahedra and Pb in ninefold coordination. The Pb2* has a stereo- chemically inactive lone pair of electrons, which causesa lowering of symmetry in the atomic structure.

INrnooucrroN OccunnnNcr There are many small depositsin the Capricorn The Anticline prospect at Ashburton Downs has an Range approximately 1000 km north of Perth, Western assemblageof secondary minerals in a weathered shear Australia. The new mineral, ashburtonite, was found at zone that cuts a seriesof shalesand graywackes.The sec- the Anticline prospect,on Mineral Claim 84, which is on ondary minerals were probably derived from a primary the Ashburton Downs pastoral lease, I 1.2 km west- sulfide assemblageincluding and ,but southwest of Ashburton Downs homestead. The speci- they are not available for study. flowever, a few residual mens used in the present description were collected by relic galena crystals can be observed in the secondary Blair Gartrell and brought to E.H.N. Gartrell had noted assemblage.The secondary assemblageconsists essen- several rare speciesand a number of unusual minerals tially ofhydrated carbonates,arsenates and sulfatesofPb that he could not identifu. His astute observations have and Cu, and to a much lesserextent, Zn and Fe. Asso- now resulted in the description of two new mineral spe- ciated with the new mineral ashburtonite are beudantite, cies:gartrellite (Nickel et al., 1989),named in his honor, brochantite, caledonite, cerussite,diaboleite, duftite, and ashburtonite, describedin the present paper. malachite, and . Nickel et al. (1989) also report The new mineral and the name were approved by the the presenceof , , , bindheim- Commission on New Minerals and Mineral Names, IMA. ite, , chenevixite, , , Cotype material is in the Collection of the Canadian Mu- , coronadite, cumengite, gartrellite, goethite, seum of Nature under catalogno. CMN 58391 and in the hematite, , , , laven- Museum of Victoria, Melbourne, under catalog no. dulan, , , , ,and ro- M40712. sasiteat this localitv. 0003{04x/91/0910-1701$02.00 r70r 1702 GRICE ET AL.: ASHBURTONITE DESCRIPTION AND STRUCTURE

Fig. l. Scanningelectron microscope photomicrograph showingashburtonite crystals elongated on [001].Scale bar is Fig.2. Crystaldrawing of ashburtonite,clinogaphic projec- 10pm. tron.

Prrvsrcll,, oprrcAl,, AND cHEMTcAL pRopERTrEs is no discernible fluorescencein either long- or short- Ashburtonite occurs as very small crystals, distinctly wave ultraviolet light. in HCI blue with no greenishtint, up to 400 pm long and 30 pm Ashburtonite decomposesrapidly concentrated concentrated wide clustered in aggregatesup to 20 mm in diameter and slowly in0.2 M HCl, l:l HNOr, and (Fig. l). Ashburtonite crystals are prismatic, elongated HrSOo. parallel to [001] with a dominant prism { I l0} and sbme- Crrnprrclr, coMProsrrroN times a minor prism { 100}, and terminated by a pinacoid {001} or a combinationof a pinacoidand pyramid {301} Chemical analysis was performed on a JEOL 733 Su- faces(Fig. 2). A dipyramidal development was noted on perprobe using Tracor-Northern 5600 automation. The some crystals. wavelength-dispersive mode was used; data reduction was Ashburtonite is transparent,with a vitreous luster and done with the Tracor-Northern Task seriesof programs pale blue streak. Crystals are very brittle, breaking with using a conventional ZAF correction routine. The oper- a conchoidal fracture and no apparentcleavage. Hardness ating voltage was l5 kV, and the beam culrent was 0.020 could not be determined becauseof the small grain size, pA. The electron beam was defocusedto 20 pm and three and the density could not be measuredaccurately; how- spectrometerswere used simultaneously to minimize de- ever, grains sink in Clerici solution (i.e., the density is composition of the sample under the electron beam. A greater than 4.07 ilcm').The calculated density is 4.69 100-s energy-dispersivescan indicated that no elements g/cm3.Ashburtonite is uniaxial *, <,r: 1.786(3)and e : with Z > 9 other than those reported here were present. 1.800(4),as determined in Na light. The lower refractive Standards used were cuprite (CuKa), mimetite (CLKa), index was determined by the oil immersion method, but sanbornite (SiKa), and crocoite (PbMa). The presenceof the immersion oils above n: 1.785 react with ashbur- COI- and OH- ions was established by infrared spec- tonite forming an opaque residue; thus a Berek compen- troscopy and by crystal-structure analysis. The result of sator was used to determine ,from which e averaginganalyses from four separatecrystals is given in was calculated. A Gladstone-Dale calculation using the Table l. The empirical formula based on 12 cations calculateddensity gives a compatibility index of -0.010, (Pb2*,cu2*,sia*)is HPbr.recuoo,sio ooo,r.03(HCo3)o(oH)4- which is regardedas superior (Mandarino, l98l). There Cl,,o. The ideal formula is HPboCuoSioO,r(HCOJ.(OH)4C1. GRICE ET AL.: ASHBURTONITE DESCRIPTION AND STRUCTURE I 703

TABLe1. Chemical composition of ashburtonite

Theoretical composition z

(wt%) of F Atomic HPboCuoSioO,, Oxide Wto/" proportions' (HCO3)1(OH)1Cl z Pbo 52.17 Pb 3.99 51.44

CuO 18.66 Cu 4.01 18.33 N sio, 14.O7 si 4.00 13.84 cl 2.28 cl 1.10 2.O4 CO,.. 10.31 HCO3 4.00 10.15 H.o't 4.22 OH 4.00 4.66 JE00.0 2800.o 1900.0 1400.0, 900,00 400.00 $/AVENUMBERS(CM-r ) 101.71 o 27.45 100.46 o: cl -0.51 -0.46 Fig. 3. Infraredspectrum ofashburtonite. 101.20 100 X-uv cRysrAlr,ocRApHy Ar\rD cRysrAL 'On basisot Pb+ Cu+ Si: 12. " Calculatedfrom stoichiometryand crystal-structureanalysis. Other STRUCTURE DETERMINATION componentsdetermined by electronmicroprobe analysis. Precessioncamera photographs show ashburtonite to be tetragonal with possible spacegroup choicesI4/m, 14 and 14.As crystals of this mineral tend to be needlelike, parallel photograph The four analysesgave totals rangingfrom I 00.5 to I 0 1.8 elongate to [001], c axis exposures wto/o. were necessarilyvery long, 5G-70 h, using Mo radiation at 1.5 kW of power. X-ray powder-diffraction data, ob- tained with a Debeye-Schenercamera having a diameter INrnnnrn ANALysrs of I14.6 mm and CuKa radiation, are given in Table 2. High-resolution infrared spectrawere recorded for the TABLE2. X-raypowder diffraction data for ashburtonite wavenumber region 400-3800 cm-' using a Nicolet 5DX Fourier transfom infrared spectrometerwith a diamond ilt" anvil cell microsampling device. Two samplesof ashbur- 110 10.065 10.2 100 tonite approximately I mg in sizewere studied with iden- 200 7.117 7.14 20 101 5.609 5.644 70 tical results; one of the spectrais shown in Figure 3. The 220 5.033 5.039 10 recorded portion between 1900 and 2400 cm-t has been 310 4.501 4.495 100 removed becauseit contains diamond spectra. 400 3.558 3.583 20 321 3.315 3.333 100 The spectrum has a large number of absorbancepeaks 420 3.183 3.192 20 resulting from the complex atomic structure of ashbur- 411 3.005 3.013 90 202 2.804 2.805 30 tonite. We cannot interpret the spectrum in detail, but 222 2.609 2.611 50 five bands give useful information on the grossaspects of 3't2 2.526 I z.szz 20 the ashburtonite structure. The complete absenceof a 440 2.516 l 530 2.441 2.439 20 band near 1600 cm-' indicates a lack of HrO in the struc- 332 2.257 2.259 20 ture. The weak peak 422 2.203 that seemsto exist in that region can 2.194 20 be attributed to adsorbed HrO. In contrast there is a broad, 611 2.',t85 ', 541 2.089 2.090 20 intense band from 2900 to 3700 cm characteristic of 512 2.060 2.058 10 the stretchingfrequency range of the OH- ion. The broad- 710 2.015 probably 103 2.014 2.010 30 ness results from contributions of OH in the 631 2.004 '1.974 bicarbonate (HCO, ) ion in addition to regular OH-. This 640 1.971 10 is also observed for nesquehonite (Farmer, 1974). The 213 1.938 1.935 10 532 1.906 1.910 10 band centeredat 1350 cm-r is characteristicof the asym- 730 1.869 1.866 20 metric stretch, ,,3mode, of the CO3- group. The shift of 72'l 1.862 z, from approximately1410 to 1350cm-' probably 622 1.811 1.812 20 takes 413 1.753 '1.751 20 place becausethe O atoms in the COI- ion of ashburton- 811 1.696 1.691 20 ite are bonded to cations other than C, which would re- 741 1.696 642 1.657 strict their vibrational modes and lower the frequencies. 503 1.655 1.656 30 In addition, this band is split into internal modes because 901 1.531 1.530 10 of lower symmetry in the CO3- group. The wavenumbers 543 1.501 930 1.500 1.499 30 are 1350and 1325cm-'. The other two bandsin regions 921 1.497 1225-850 750450 633 1.468 and cm-r are very complex, as they 1.466 20 contain contributions from several coordination com- 851 1.465 860 1.423 1.422 10 plexes,notably the SiOotetrahedron and its polymerized 912 1.397 1.399 10 tetrahedral ring, the Cu octahedron, and the Pb polyhe- 813 1.333 1.333 20 dron. 862 1.290 1.288 30 1704 GRICE ET AL.: ASHBURTONITE DESCRIPTION AND STRUCTURE

Tagle 3. Postitional coordinates and thermal parameters 1x 100, A'z)for ashburtonite z uu u"" us U"" ur" ur" un -0.01(3) Pb 0.21321(4) 0.03767(4) 0 1.68(4) 0.80(3) 1.s1(2) 0 0 1.33(2) V4 V4 V4 1.48(s) 1.04(8) 1.12(7) -0.14(6) 0.22(6) -0.74(6) 1.22(41 Cu -0.0803) Si 0.1167(3) 0.1064{3) v2 0.86(19) 0.58(19) 0.86(15) 0 0 0.77(10) -l c 0.438(2) 0.8s9(2) 0 2.1(1.1 ) 6.8(1.5) 4.90.1) 0 0 .0(1.0) 4.6(7) 0.724s(9) 0.8(3) 0.9(3) 1.6(3) 0.4(3) -0.4(3) -0.6(2) 1.1(2) 01 0.1637(5) 0.14s5(4) -0.1(3) 02 0.3027(6) 0.1805(6) 0 0.4(5) 1.3{s) 1.3(4) 0 0 1.0(3) 0.0062(7) 0.1305(7) v2 0.3(5) 2.9(6) 2.6(s) 0 0 -0.1(4) 1.9(3) 03 - 04 0.3505(12) 0.8641(11) 0 6.2(1.1) 6.2(1.1) 6.7(9) 0 0 1.1(9) 6.4(6) -0.5(6) 05 0.4839(8) 0.85s6(8) 0.1782(15) 5.7(8) 8.1(9) 10.2(e) 2.3(71 - 1.8(7) 8.q4) cr 000 1.6(2) 1.6(2) 2.2(3) 0 0 0 1.8{2) Note..Temperaturefactors are of the form expl-2r2(Uuh2a'2 + lJ22kb-2+ . . . + 2lJehka'b')1. Estimatedstandard deviationsare in parentheses.

The refined unit-cell parameters are q: 14.234(7)and c Mann (1968)and Cromer and Liberman (1970),respec- : 6.103(5)A wittr V : 1236(l) A' and Z : 2. tively. From the E map the positions of the Pb, Cu, Si, For the intensity-data measurements,a prismatic crys- and most of the O atoms were readily determined. The tal fragmentmeasuring 0.015 x 0.04 x 0.08 mm (CMN difference-Fouriermaps of this initial model showed ad- no. 58391,xl 7) was mounted along I l0]. Intensitydata ditional atomic sites. were collected at CANMET. Ottawa, on an Enraf Nonius Table 3 contains the final positional and anisotropic CAD-4 single-crystal diffractometer operated at 52 kY displacementparameters; Table 4,t the observedand cal- and 26 mA with gaphite-monochromated MoKa radia- culated structure factors; and Table 5, the selectedinter- tion. Data measurementand reduction were done using atomic distancesand angles.The final stagesof the least- the NRCVAX packageof computer programs (Gabe et squaresrefinement involved a conversion to anisotropic al., 1985).A setof 8l reflectionspermuted four ways, +ft temperature factors and the addition of a weighting '. at +20, was used to refine the cell parameters: 4 : schemeof [o'z(F)] This resulted in final residual indices 14.1852(8)and c : 6.0759(8)A. I fuU sphereof data of R : 3.50/oand R*: 2.4o/ousing 762 observedreflec- was obtained to 20 :60" assumingan /-centered lattice. tions to refine the 65 least-squaresparameters. An ex- The intensities were corrected for Lorentz and polariza- tinction correction was tried, but it did not improve the tion eflects, and a Gaussian absorption correction (pr : refinement. 315 cm-t) was applied. The transmission factors ranged Each ofthe possible spacegroups was refined using all from 0.37 to 0.61. Of the 8059 measuredintensities, 968 the intensity data and the weighting scheme prescribed are independent, and 760 of these are observed [.F > by Hamilton (1965).The Rg for eachof the spacegroups 5.0o(F)1.It is significant that the three standard reflec- 14/m, 14. and 14 are 2.61, 2.51, and 2.45, respectively. tions decreasedin intensity by 3o/oover the l2-days of Using Hamilton's (1965) R-factor ratio test, the statistics the experiment. indicate a slight preferencefor the 14 spacegroup but this The structure was solved using direct methods, and the ' A copyof Table4 maybe orderedas Document AM'91-469 package refinement was done with the SHELXTL PC of from the BusinessOffice, Mineralogical Society of America,I130 programs. Scatteringcurves for neutral atoms and anom- SeventeenthStreet NW, Suite 330, Washington,DC 20036, alous dispersion correctionswere taken from Cromer and U.S.A.Please remit $5.00in advancefor the microfiche.

TABLE5. Selected interatomic distances (A) and angles (') in ashburtonite Si tetrahedron C triangle si-01 1.616(6)x2 c-04 1.24(3) si-03 1.605(10) c-05 1.27(21x2 si-03 1.609(10) Mean 1.26 Mean 1.611 04-05 2.18(21 121(1\x2 01-03 2.63(1) 109.3(3)x2 05-05 2.16(21 117(21 01-03 2.5e(1) 106.9(3)x2 01-01 2.73(1) 115.1(s) Cu octahedron 03-03 2.62(1) 109.3(8) Cu-01 1.929(6)x 2 Cu-02 1.959(6)x 2 Pb polyhedron Cu-04 2.638(13)x 2 Pb-01 2.374(61x2 01-o2 2.63(1) 94.7(3)x2 Pb-o2 2.391(9) 01.02 2.86(1) 85.3(3)x2 Pb-03 3.315(4)x2 01-04 3.1s(1) 94.1(41x2 Pb-04 3.13s(16) 01-04 3.1s0) 85.9(4)x2 Pb-05 2.829('11)x2 02-04 3.19(1) 86.6(3)x2 Pb-c1 3.071(1) 02-04 3.19(1) 93.4(3)x2

Note.'Estimated standard deviations are in parentheses. GRICE ET AL.: ASHBURTONITE DESCRIPTION AND STRUCTURE I 705

r------a

a Fig. 5. An inclined a axis projectionof the ashburtonite structureshowing ribbons of Cu octahedra,four-membered Si tetrahedralrings, and CO, groupsin the c axis channels.Pb atomsare smallopen circles, and Cl atomsare larger open cir- cles.

Pb plays a major role in this structure by bonding to all the major polyhedra, Si, Cu, and C. Figure 6 shows this odd, large Pb'?*coordinate complex, which has five regular Pb-O bond lengths varying from 2.38 to 2.84 A Fig. 4. A c axis projectionof the ashburtonitestrucrure on one side of the polyhedron and three longer Pb-O showingfour-membered Si tetrahedralrings and (stippled)Cu bonds (3.14-3.31 A) and a Pb-Cl bond (3.07 A) on the octahedra.Pb atomsare filled circles, Cl atomsare open circles, other side. Probably the long-bonded portion ofthe poly- and CO, groupsare shadedtriangles with planesapproximately hedron has a lone pair ofelectrons that spread out these parallelto (100). bonds. In fact, the stereochemically inactive lone-pair electronsof Pb effect a major shift in the Pb position and destroy the mirror planesof point symmetry 4mm estab- result cannot be considered significantly better than that lished by the four-membered tetrahedral ring of Si. This of I4/m in view of the large systematic errors involved displacement of Pb2* from higher symmetry sites has been in the absorption correction of the intensity data. The noted in hyalotekite (Moore et al., 1982), joesmithite dipyramidal morphology of some crystalsindicates point (Moore, 1988),and beudantite(Szymafiski, 1988). group 4/m, which suggeststhat the preferred spacegroup Liebau (1985) points out the importance of the pres- should be I4/m. All of the structure results tabulated in enceofhighly electronegativecations such as Pb and Cu, this paper will therefore be for spacegrotp 14/m, but the which inhibit silicate chain formation in favor of a tight structure model for spacegroup 14 has some appealing ring complex. These cations effectively reduce the elec- aspectsthat will be discussedlater. trostatic repulsive forces between adjacent SiOo tetrahe- dra, thus stabilizing the ring formation. Common ele- Dnscnrp"rroN AND DrscussroN oF ments that would inhibit this structure type are Mg, Mn, THE STRUCTURE The basic structural motif of the ashburtonite structure is a four-membered, tetrahedral silicate ring (Fig. 4). Very few mineralshave this type ofring structure.Liebau (1985) lists six minerals (papagoite,kainosite, joaquinite, tara- mellite, baotite, and nagashimalite) and three synthetic phases[HKSi3Orr, KrScSirO.(OH), and Pb,SiOo].Finger et al. (1989) recently described another synthetic phase and noted that in BaCuSirOuthe four-membered ring has point symmetry 2mm, which is higher symmetry than any so far reported for structuresofthis class.In ashbur- tonite, the silicate ring has point symmetry 4mm that seemsto dominate the overall topology of the structure. The [SiO,] tetrahedra are cross linked by octahedrally coordinated Cu. The Jahn-Teller distortion in the Cu oc- tahedron is very evident, with Cu-O bond lengthsof 2.62 A along the apices,and pairs of 1.93 and 1.96 A bond lengths in the equatorial plane. The Cu octahedra form edge-sharingribbons parallel to the c axis (Fig. 5). Fig. 6. Pb polyhedron in ashburtonite structure. 1706 GRICE ET AL.: ASHBURTONITE DESCRIPTION AND STRUCTURE and Fe, all notably minor in concentration in the ash- tures determined. Within the earth's weathering profile burtonite assemblageand completely absent in ashbur- there are wide Eh and pH ranges compatible with the tonite itself. formation ofbicarbonates; perhaps their apparent rarity The Cl- ion lies on the tetrad axis midway between in numbers of speciesis only becausethe techniquescom- silicate rings (Fig. 5). It is located at the center ofa square monly used to analyzeminerals do not differentiate this plane of four Pb atoms similar to that in the taramellite chemical class. A good analysis is re- structure (Mazzi and Rossi, 1980).Similar to Pb and Cu, quired to recognizea bicarbonate, and this paper further the highly electronegativeatom Cl effectively stabilizes supports this method as a valid and useful chemical an- the four-membered silicate ring by reducing the average alytical technique (Hawthorne and Grice, 1990).Some of negativecharge on each SiOotetrahedron (i.e., an electron the details of proton distribution could be resolved with sink). neutron diffraction studies,but the small crystal size pre- Although the number and location of H atoms could cludes this type of experiment at present. not be determined from Fourier synthesis,bond-valence calculations for each O site, based on the constants of AcrNowr,nlcMENTS Brown (1981), helped delineatetheir distribution. The grateful for cooperation and sup- bond-valencesums for the O atomsare Ol 2.04,02 1.32, The authors are to the following their port in this project: J.T. Szymaiski, CanadaCentre for Mineral and En- 03 2.26,04 1.95,and 05 1.58vu. This leadsus to con- ergy Technology , Ottasva, for permission to use the single-crystal diffrac- clude that 02 is an OH anion and that 05 has an H atom tometeq Y. Lepage, National Research Council of Canada, Ottawa, for shared in part between two symmetry related O atoms providing computer facilities; R.S. Williams, Canadian Conservation In- bonded to C, making a bicarbonategroup If the stitute, Ottawa, for the infrared analysis; B.W. Robinson, Commonwealth [HCO']-. Scientific and Industrial Research Organization, Perth, for electron-mi- spacegroup is lowered in symmetry to 14, these two O croprobe analysis;T.S. Ercit, Canadian Museum ofNature, for assistance atoms are no longer symmetry related by the mirror plane, with the electron microprobe analysis; and R. Dinn, Canadian Museum and the bond-valence sum is markedly lower for one of of Nature, Ottawa, for typing the manuscript. The reviews of L.W. Finger them, 0.91 vs. 1.70vu. This is the one featurethat favors and F.F. Foit, Jr. greatly improved this manuscript. the 14 model as mentioned previously.Based on the above information, the simplest chemical formula is PboCuoSio- RnrnnrNcns crrED O,r(HCO3)4(OH).CI,but this formula needsone addition- Brooks, R., and Alcock, F.C. (1950) Crystal structure of ammonium bi- al positive chargefor chargebalance. From bond-valence carbonate and a possible relationship with ammonium hypophosphate. calculations, it appears that Pb (1.99 vu) and Cu (2.07 Nature, 166, 435436. Brown, I.D. (1981) The bond-valencemethod: An empirical approachto vu) are nearly saturated. It is quite possible that the chemical structure and bonding. In M. O'Keefe and A. Navrosky, Eds., "missing" positive chargeis a proton in the channelsas- Structure and bonding in crystals, p. l-30. Academic Press, New York. sociated with the bicarbonate group as a hybrid of [HCOr]- Cromer, D.T., and Liberman, D. (1970) Relativistic calculation of anom- Physics, and [HrCOr]. There are reasonsfor proposing this inter- alous scatteringfactors for X-rays. Joumal of Chemical 53, l l-l esting hybrid. Both 89 898. 04 and 05 have large displacements Cromer, D.T., and Mann, J.B. (1968) X-ray scatteringfactors computed on the order of those expectedfor OH, and both of these from numerical Hartree-Fock wave functions. Acta Crystallogaphica, O atoms have low bond-valence sums. In the 14 model 424,32r-324. all three bicarbonate O atoms have similar characteris- Farmer, V.C. (1974) The infrared spectraof minerals. Mineralogical So- p. tics. The H ions probably do not alwaysbond to the same ciery Monograph 4,539 Mineralogical Society,London. Finger, L.W., Hazen, R.M., and Hemley, R.J. (1989) BaCuSi,Ou:A new O atom, but one or two could be shared at each bicar- cyclosilicate with four-mernbered tetrahedral rings. American Miner- bonate group. alogisr, 74, 952-955. In Figure 4 the trigonal plane of [COr] in the bicarbon- Gabe, E.J., I€e, F.L., and kpage, Y. (1985) The NRCVAX crystal struc- ate group is not evident as it is approximately parallel to ture system. In G.M. Sheldrick, C. Kruger, and R. Goddard, Eds., Data structure determina- (100) Crystallog,raphic computing 3: collection, and hence appearsas a line in this projection. Yet tion, proteins and data bases,p. 167-174. Clarendon Press,Oxford. Figure 4 does show clearly how large this channel is, and Hamilton, W.C. (1965) Significancetests of the crystallographicR factor. although the CO3anion is anchored through 04 to the Cu Acta Crystallographica,I 8, 502-5 I 0. octahedron on one end, the other ends are only loosely Hawthorne, F.C., and Grice, J.D. (1990) Crystal structure analysis as a Application to first-row elements. Cana- bonded to Pb through two 05 atoms. The large thermal chemical analytical method: dian Mineralogist, 28, 693-7 02. displacement factors for the atoms involved (C, 04, and Liebau, F. (1985)Structural chemistry ofsilicates, 347 p. Springer-Verlag, 05) show how loosely bonded it is. The bond distanceof Berlin. O5-O5 of 2.63 A acrossthis open channelis good evi- Mandarino, J.A. (1981) The Gladstone-Dalerelationship: Part IV. The dence for H bonding between bicarbonate groups. This compatibility concept and its application. Canadian Mineralogist, 19, 441450. has been noted in the crystal structuresof nahcolite (Za- Mazzi, F., and Rossi,G. (1980)The crystal structwe of taramellite.Arner- chariasen, 1933) and teschemacherite(Brooks and Al- ican Mineralogist, 65, 123-128. cock, 1950) where H-bonded bicarbonate groups form Moore, P.B. (1988) The joesmithite enigma: Note on the 6s '?Pb2*lone chains. Two carbonateanions shareone H (Pertlik, I 986) pair. American Mineralogist, 7 3, 843-844. (1982) in trona. Moore, P.8., Araki, T., and Ghose,S. Hyalotekite, a complex borosilicate: Its crystal structure and the lone-pair effect of Pb(II). Very few minerals are described as bicarbonates,and American Mineralogist, 67, 1012-1020. only a small portion of thesehave had their crystal struc- Nickel, 8.H., Robinson, B.W., Fitzgerald,J., and Birch, W.D. (1989) Gar- GRICEET AL.: ASHBURTONITEDESCRIPTION AND STRUCTURE L7A7

trellite, a new secondaryarsenate mineral from Ashbunon Downs, W.A. [(AS,S)O4]r(OH)6.Canadian Mineralogist, 26,92T932. and Broken Hill, N.S.W. Australian Mineralogist,4, 8!89. Zachariaseq W.H. (1933) The crystal lattice of sodium bicarbonate, Pertlik, F. (1986) Ein Vergleich von Ergebnissen routinemlBiger Struk- NaHCOr. Joumal of Chemical Physics, 1,6344t9. tubestimmungen mittels R6ntgen-BZW. Neutronen-Einkristalldaten arn Beispiel der Trona, N3H[CO3]2.2HrO. Mitteilungen der Osterrei chischenMineralogischenGesellschaft, l3l, 7-13. Meruscnrsr RECETvEDNoveMsER 9, 1990 Szymafski, I.T. (1988) The crystal structure of beudantite, Pb(Fe,AI)3- MaNuscnrrr AcErrED Me,v 21, 1991