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American Mineralogist, Volume 73, pages 405-412, 1988 Ingersonite,a new calcium-manganeseantimonate related to pyrochlore, from Lflngban, Sweden Pnrn J. DuuN Departmentof Mineral Sciences,Smithsonian Institution, Washington,D.C. 20560,U.S.A. DoNar,o R. Pracon Department of Geological Sciences,University of Michigan, Ann Arbor, Michigan 48109, U.S.A. Ar,aN J. Cnrnor,r, Cnnrs J. SuNr,nv Department of Mineralogy, British Museum (Natural History), London SW7 5BD, England Assrnacr Ingersonite,CarMnSboO,o, is hexagonal,space group P3m, P32, P3m, P3r2, or P3r2, with a : 7.287\3), c : 17.679(\ A, V: 813.0(6) fi2,7 : 3. The strongestX-ray diffrac- tions [d (I/IJ (hkl)] are 2.97t (r00) (222), 1.55 (80) (226), r.819 (70) (440), s.92 (60) (111),and 3.10 (50)(113). The chemicalcomposition, determined by microprobeanalysis, is FeO 0.2,MgO 0.0,CaO 15.9,SbrO5 74.'7,MnO 9.4, sum 100.2wto/o; F is present,and the content varies from 1.4 to 3 wt0/0.These data, combined with the cell parameters, indicate that ingersonite is isotypic with pyrochlore and romeite. Ingersonite occurs as irregular aggregatesof subhedral crystalswith calcite, clinohumite?, jacobsite, and an un- named mineral at the LAngbanmine, Viirmland, Sweden.It is transparent to translucent, has a vitreous luster, and is uniaxial negative.In reflectedplane-polarized light, it is light gray, sometimeswith a slight yellowish cast imparted by characteristicyellow and white internal reflections.Luminance values [1(o/o)],computed from visible spectrumreflectance measurements,are about l0o/oin air and 2 to 3o/oin Zeiss oil (N" 1.515).Indices of refraction calculatedfrom the reflectancespectra are grven; r < v. regular yellow aggregates,few in number; hence, it is a INrnooucrroN rare mineral. More detailed data on the texturesare given In 1985, Roland Eriksson of LAngban, Swedencalled below. There is much visual similarity betweeningerson- an unknown yellow mineral to the attention of one of the ite and other yellow minerals from Ltrngban,so it is pos- authors (P.J.D.). The X-ray powder photograph of this sible that some specimensof ingersonite may have been mineral resembledthat of romeite, but exhibited distinct misidentified. However, intensive searchesof systematic differences.A detailed examination of this new phasein- museum colllections failed to find additional ingersonite dicatedthat it is hexagonal,with Mn:Ca near l:3, and is specrmens. a new mineral species.We have named this new mineral speciesingersonitein honor of Dr. H. Earl Ingerson,dis- CnnN4rcar coMPosITIoN tinguishedgeochemistofSwedishancestry,andpresently There was insufficient material for a wet-chemical ProfessorEmeritus at the University of Texas.The species analysis, and ingersonite was chemically analyzed using and the name were approved by the Commission on New electron microprobes. A wavelength-dispersivemicro- Minerals and Mineral Names, IMA. Type material is de- probe scanindicated the absenceof elementswith atomic posited in the Smithsonian Institution under catalogue number greaterthan 8 other than those given below. The number 163012, and at the British Museum (Natural resultant analyses,together with standardsused, are pre- History) under cataloguenumber BM I 986, 410:E.ll77 . sentedin Table I . occunn'NcE s"I?:;?Jlil,H:'H.::,l'.T:i.ll,i';Ji'll,l'l#:i.TiJ; Ingersonite was found on the dumps at the Ltngban ofequal rank, one having eightfold coordination and the mine, Viirmland, Sweden,and nothing is known of the other octahedralcoordination. The ideal formula ofpyro- specificgeologic relations of its occurrence.The sole sam- chlore, as representedby most synthetic phaseswith the ple we have studied,5 x 4 x 2 cm in size,consists of pyrochlorestructure (Subramanian et al., 1983)and ap- fine-grainedcalcite with two opaque minerals facobsite proachedby most natural pyrochlore-family minerals, is and filipstadite) as very fine grained crystals irregularly ArB2Or. The A site is commonly occupied by large cat- distributedthroughout the calcite.The specimenhas no ions such as Cd2*, Ca2+,and Mn2+, whereasSbs+ occu- preferred orientation. Ingersonite occurs sparsely as ir- pies the octahedrally coordinated B site. Becausethe an- 0003-o04x/88/0304-{405$02.00 405 406 DUNN ET AL.: INGERSONITE TABLE1 Microprobeanalyses of ingersonite reflectionsoccurred in the X-ray diffraction pattern. Pyro- chlore, and specificallythe chemically relatedspecies rom- Grain1. Grain2. Grain3-' eite (seebelow), has a face-centeredunit cell ofequivalent 15.9 167 19.9 dimensions. These relations, in combination with the MnO 9.4 9.4 9.1 Mgo 0.0 00 n? chemicaldata, therefore imply that ingersonitehas a struc- FeO 00 0.3 ture that is derivative from that of romeite. Exceptions sbrou 74.7 73.8 72.6 Total 100.2 99,9 102.2t to the systematicextinction rule that are not compatible . with any space group were not detected. Becausesuch CambridgeInstruments Microscan lX electronmicroprobe, 20 kV. presence Standards:Pure Sb, Al, and Mn, CaF, MgSiOo,MgCrO", and FeS. patterns often imply the of twinning, the dif- '. ARL-SEMoelectron microprobe, 1 5 kV, 0 025-pAsample current. Stan- fraction patterns were examined for twinning, but none dards:synthetic Sb,O3 (Sb), manganite (Mn), fluorapatite (F), hornblende, was detected. (Ca, Mg, Fe). Data corrected with a modified version of the irActc-4pro- gram The Laue symmetry is 32/m, the lattice is primitive, t F is present,but inhomogeneous;value is 1.4to 3 (+0.3) wt%. Total and the presenceofdiagnostic reflectionsshows that there not corrected for o = F. is no c glide. However, the general systematicextinction rule describedabove includes 00/ reflections as a special case;this suggeststhat the apparently extinct 00/ reflec- alytical data for ingersonite initially seemedto be tions may be weak but unobservable,as is true for the consistent with these relations, they were normalized to more generalset of reflections.With this ambiguity taken 24 total A and B cations, the sum correspondingto the into account,the list of possiblespace groups is P3m, cell contents(see xno data below) for the ideal pyrochlore P32,P3m, P3,2, or P3,2. composition.Analysis 3 in Table I, which was obtained The unit-cell parametersla : 7.287(3),c : 17.679(9) from the samecrystal usedfor single-crystalstudies, gave A, v : 813.0(6)A'1 were refinedusing powder data ob- rise to the formula (Cano, Mn, nr)":,,(Sb,, o, Mno * Mgo,n- tainedwith a I 14.6-mm-diameterGandolfl camera, pow- F€0,,)":,,nnOo, ,,F,, where)r is lessthan 4. F is variable dered sample,NBS Si as an internal standard,and CuKa (Table l) and not includedin our calculations. X-radiation. The powder pattern of ingersonite(Table 2) The smaller Mg and Fe ions are assumedto occupy the was indexed by analogy with the pattern of romeite, but smaller, octahedrally coordinated site, as there is a defi- by taking the splitting ofreflections due to the deviation ciencyof Sb atoms.Because the amounts of Ca and Mn from cubic symmetry into account. Several reflections initially assignedto the A site exceededthe allowed sum, occurring in the pattern ofingersonite, but not in that of the excessMn was also assignedto the B site, as Mn is romeite, are readily indexed on the calculatedpattern of smaller than Ca and is more likely to assumeoctahedral romeite. In addition, the single-crystaldiffraction inten- coordination. sity relations implied that only the intense substructure Natural members of the pyrochlore family commonly reflections(i.e., those correspondingto the romeite unit have defectson the A, B, and anion sites.In addition, Sb cell) should be observable in the powder pattern. The may be in part trivalent, as proposed for stibiconite (Vi- reflectionswere indexedusing the initial valuesofa and taliano and Mason, 1952) and confirmed by M<lssbauer c as obtained from single-crystaldiffraction photographs. studies(Brisse et al., 1972)i as such, it may occupy the A A sufficientnumber of unambiguouslyindexed reflections site. It is therefore not possibleto normalize the formula were identified for least-squaresrefinement of the lattice to any specific cation or anion sum with complete con- parameters.However, even with the absenceof super- fidence. The cell contents as calculated above (assuming structure reflections in the powder pattern, there is mul- no cation vacancies)are compatible with the pyrochlore tiple indexing of many reflections.It is also interesting to formula, giving the ideal formula (CarMn)Sb.O,oforZ: note that becausere-indexing of the face-centeredpyro- 3. Alternative calculationsbased on other cation or anion chlore lattice on hexagonal axes gives rise to a rhom- sums, with or without vacancies,all give rise to detailed bohedral lattice, the presenceof substructurereflections formulae that are only slightly different from that given in the powder-diffraction pattern implies that ingersonite above, and all are consistentwith the sameidealized for- is pseudo-R-centered. mula. PuvsIc,q,r, PRoPERTIES X-n^q.vcRYSTALIoGRAPHY Ingersonite occurs as massive aggregatesof subhedral Ingersonitewas studied using Weissenbergand preces- crystals,2-3 mm in diameter,composed of 0.3-mm crys- sion single-crystalX-ray methods. The diffraction pho- tals intimately associatedwith filipstadite, a new Mn-Sb tographs display an unusual pattern of systematic ab- spinel-groupmineral (Dunn et al., 1988).Ingersonite is sencesin that only every third reflection along c* is brownish yellow, as is its streak. The luster is vitreous. observedfor rows having h,k: 2N. Suchreflections are Micro-indentation

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