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Home , Manganese oxide, Oxide mineral, Ramsdellite, Todorokite

American Mineralogist, Volume 64, pages I199-1218, 1979

The tetravalent manganeseoxides: identification, hydration, and structural relationships by infrared spectroscopy

RussBrr M. Porrnn'AND GpoRcn R. RossueN Division of Geologicaland Planetary Sciencef Califurnia Institute of Technology Pasadena,Califurnia 9I 125

Abstract

A compilation of the infrared powder absorptionspectra of most naturally occurring tet- ravalent and trivalent manganeseoxides is presentedwhich is intended to serveas a basisfor the spectroscopicidentiflcation of theseminerals in both orderedand disorderedvarieties, in- cluding those too disorderedfor X-ray diffraction studies.A variety of synthetic oxidesare also included for comparisonto the natural phases.The samplesinclude: aurorite, ,, buserite, chalcophanite,coronadite, ,, hausman- nite, , lithiophorite, maoganite, manganese(Ill) manganate(IV), , manjiroite, marokite, , partridgeite, , quenselite,rancieite, ,ro- manechite, manganese(Il,flI) manganate(Iv), , and woodruffite. The spectraindicate that well-orderedwater occurs in ramsdellite,chalcophanite, and most ro- manechites.Disordered water is observedin the spectraof nsutite,, birnessite, to- dorokite, buserite,and rancieite.The infrared spectraof well-orderedtodorokite, birnessite and rancieite differ which indicatesthat they possessdiflerent structuresand should be re- garded as distinct species.Much variation is observedin the spectraof pyrolusites, nsutites,birnessites, and todorokiteswhich is interpretedas arising from structural disorder. Spectraltrends suggest that todorokite,birnessite and rancieitehave layered structures.

Introduction crystal structures and structural relationships. The finely-particulate and disordered nature of X-ray powder diffraction patternsare the only struc- manganeseoxides in many of their concentrationsin tural data available on severalof the impor- the weatheringenvironment has made identification tant in the weatheringenvironment, and thesegener- of their mineralogy by means of X-ray diffraction ally show lines which are few in number, broad, and difficult and sometimesimpossible. Characteristic X- sometimesvariable in position. This has causedun- ray powder diffraction lines are frequently broad, in- certainty in the structural relationships among syn- distinct, or absent altogether and do not serve as a thetic and natural samplesand a consequentcon- satisfactorybasis for identification. The frequent oc- fusion in their classification. currence of silicate phasesadmixed with the low- This work will show that infrared (IR) spectros- temperaturemanganese oxides is an additional com- copy is often a necessaryalternative and generally a plication becausetheir X-ray lines can sometimesbe useful supplement to X-ray diffraction for mineral- confusedwith those of the manganeseoxides. ogical analysisof the manganeseoxides. Because it is Problems of particle size and disorder are a char- sensitiveto amorphous componentsand those with acteristic of pure manganeseoxides and have been short-rangeorder as well as to material with long- responsiblefor our poor understandingof manganese range order, IR spectroscopyyields a more complete and reliable descriptionof materialssuch as the man- I Presentaddress: Owens-Corning Fiberglas Corporation, Gran- ganeseoxides, where crystalline disorder may be ex- ville, Ohio 43023. pected.In addition, it is sensitiveto the structural en- 2 Contribution N o. 3126. vironment of the hydrous components, which is 0np3-{0/'X/7 9/ I I I 2- I 199$02.00 POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES frequently diagnosticof the manganeseoxide mrner- Appendix figures are indicated by an "A" or "B" fol- alogy. lowing the figure number.' The intensities of IR BecauseIR spectroscopyis not a primary struc- spectramay vary by a factor of 2 or 3 due to differ- tural technique like X-ray diffraction, it is necessary encesin sample particle size and dispersion in the to "calibrate" it against well-crystallized materials pellet. For this reason we have presentedthe IR whose mineralogy has been previously determined spectra at concentrationssuch that all spectrahave by X-ray diffraction. Once a mineral's characteristic the samemaximum intensity in the 1400cm-' to 200 IR spectrum has been determined, it can then be cm-' region. Each spectrumin the 4000cm-'to 1400 usedto identify whether that phaseis presentin more cm-' region is presentedat 4 times the concentration disorderedsamples. of its lower energy spectrum. The presentationin- More than 20 predominantly tetravalent manga- tensitieslisted in the figure captionsallow the origi- nese oxide phasesare recognizedas valid mineral nal intensity of the spectrato be calculated.The pre- species.X-ray criteria for the identification of the sentation intensity is 100 times the intensity in the well-crystallizedoxides are well established(Cole et figure divided by the intensity measuredusing the al., 1947;Burns and Burns, 1977a).This paper pre- standardpreparation techniques (Section 2). sentsthe basisfor determinationof their mineralogy Experimentaldetails by IR spectroscopy.The IR spectraof many of the manganeseoxides have been published (Gattow and Purity and mineralogy were determinedby X-ray Glerrser, l96la, b; Glemser et al., 196l; Moenke, powder diffraction using CrKa radiation and a 1962;Yalarelhet a1.,1968;Agiorgitis, 1969; Kolta el Debye-Scherrercamera. The IR spectrum of some al., l91l; van der Marel and Beutelspacher,1976), is so distinctive that after an initial correla- but the quality of the data are generally too poor to tion was made betweenthe X-ray diffraction pattern show clear differencesamong the oxides. Using im- and the IR spectrum, further X-ray work was not proved instrumentation and sample preparation needed.When necessary,qualitative chemicalanaly- techniques,we have found that the differencesin the sis was usedin addition to X-ray diffraction to deter- IR spectra of the tetravalent manganeseoxides are mine mineralogy. sufficiently diagnostic to permit their identification in IR spectra were obtained with a Perkin-Elmer manganeseoxide concentrationsof the natural envi- model 180spectrophotometer on 2.0 mg of powdered ronment evenwhen the oxidesare highly disordered. sampledispersed in TlBr pelletsfor the 4(XX)cm-' to We have usedthese spectra as the basisfor the deter- 1400cm-' region and on 0.5 mg in TlBr and KBr pel- mination of manganesemineralogy in a variety of lets for the 1400cm-' to 200 cm-' region. Pelletsof occurrences including desert varnish, manganese 13 mm diameter were pressedfor I minute at 19,000 dendrites, stream deposits, and (Potter psi under vacuum. Pellets were prepared without and Rossman,1979a,b, c). evacuationto verify that dehydration of the manga- This paper also contains the results of research nese oxide did not occur under these conditions. into somefundamental problems of tetravalentman- SinceKBr is hygroscopic,it was not usedin the 4000 ganeseoxide mineralogy.We have usedour spectro- cm-' to 1400cm-' region,where water and scopic results in conjunction with a variety of other absorptionoccurs. TlBr is preferableto KBr because techniquesto investigatestructural variations within it is non-hygroscopic.Also, becauseits refractive in- the manganeseoxides, to addressquestions about the dex better matchesmost manganeseoxides, it gives doubtful structures,to proposestructural models for spectra of better quality. The figures presentedare structureswhich are as yet unknown, and to test the from TlBr pellets. Where the corresponding spec- validity of synthetic materials as analogsof natural trum in KBr differs significantly,it is included in Ap- samples. pendix B. A vacuum dewar with KBr windows was The presentationof theseresults follows the classi- used to obtain IR spectraat liquid nitrogen temper- ficationscheme of Burns and Burns (1975,l977a,b), ature in the 4000 cm-' to 1400cm-' region. Qualita- which is based on the nature of the polymerization of tive chemical analyseswere done with an SEM MnOu units, in which six oxygenssurround a central 3 manganesecation in approximatelyoctahedral coor- To receivea copy of Appendic.esA and B and a table of IR band positions, order Document AM-79-ll7 from the Business dination. For each structure representativespectra Office, Mineralogical Society of America, 2000 Florida Avenue, are included with the text. Spectraof other samples NW, Washington,D. C. 20009.Please remit $1.00in advancefor are containedin Appendix B as indicated in Table l. the microfiche. POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES l20l

equipped for energydispersive X-ray analysis.Man- the resolution of bands 3,4, and 5 improves,and the ganeseoxidation statewas determinedby room tem- intensity of band 3 growswith respectto band 4. perature dissolution in excess0.05M Fe2* in 0.5M All the pyrolusite powder diffraction patternscon- HrSO4followed by back titration of excessFe2* with tain linesat 3.40,2.63,2.32,1.78, and l.7lA. These 0.002M KMnOo and spectrophotometricdetermina- cannot be indexed on the tetragonal pyrolusite cell tion of total Mn as MnO;. This procedureis a modi- nor on a superlatticeof it. They can all be attributed fication of that of Moore et al. (195O).Far-infrared to manganiteand accountfor its four strongestlines. spectrain the region 200 cm-' to 35 cm-' were ob- The +3.99 manganeseoxidation state of pyrolusite tained from a petroleum jelly mull of l0 mg of #l I limits its possiblemanganite contamination to I samplespread on a polyethyleneplate. percent. Although other pyrolusite samples could have up to 8 percent ,their unindexed X- ray lines are not measurablystronger than those The chain structures:pyrolusite, nsutite, ramsdellite of pyrolusite #1. IR sp€ctroscopylimits the amount of Pyrolusire manganite impurity to less than 5 percent for all samples,based on the intensity of the band near I100 Two structural forms of pyrolusite are thought to cm-'. This feature may alternatively be attributed to exist (de Woltr, 1959):a tetragonal form, which is someother hydroxide impurity or to an overtone characteristicof pyrolusite of primary origin, and an of the intense absorption at lower wavenumber.At orthorhombic modification characteristicof pyrolu- present it seemslikely that most pyrolusite samples site formed by alteration of manganite.A single-crys- contain a small amount of manganiteimpurity, but tal X-ray structural determinationhas not been done we do not feel that the evidenceis conclusive. for pyrolusite. The tetragonal structure (Fig. l) is The variation in the pyrolusite IR spectraof Fig- basedon X-ray powder diffraction data. MnOu octa- ure 3 is representativefor pyrolusite samplesin gen- hedra shareedges to form singlechains linked to one eral and is a problem in its own right. The primary another by sharedvertices along the c axis. De Wolff differenceamong the spectrais the position and rela- postulatedthe existenceof an orthorhombic modifi- tive intensity of band 3. Farmer (1974) has consid- cation from broadening of several X-ray powder ered the effect particle shape would theoretically lines. Electron microscopyhas revealedoriented la- have on the IR spectraof , which is isostruc- mellar poresin secondarypyrolusites which could be tural with pyrolusite and has a spectrumsimilar to it. responsiblefor this distortion (Champness,197l). He suggestedthat shapemay be the causeof large The X-ray powder patternsof Figure 2 confirm the variations in the IR spectraof different powderedru- existenceof an orthorhombic pyrolusite.The pyrolu- tile samples.The major variation in going from a site patterns are arranged in order of increasing platy to a needle-likemorphology is predictedto be a broadnessof the following lines (indicesin parenthe- decreaseof severalhundred wavenumbersin the po- sis):2.204 (200),1.97 (210), 1.62 (2ll), 1.391(310), sition of band 3, which is similar to the variationswe 1.305(301), l.2O (202). The (301) line is superim-, observe for pyrolusite. Although scanning electron posedon that of (l l2), which doesnot split. For py- microscopydid show variation in particle shapefrom rolusite #4 severalof theselines are clearly-resolved needlesto equant particles, this variation could be doublets, and the overall pattern can be indexed to generated for a single sample by different grinding an orthorhombic cell bearing the following relation techniqueswith no effecton the position of band 3. It to the undistortedpyrolusite cell: thus appearsthat particle shapeis not responsiblefor tetragonal orthorhombic the variation in pyrolusite IR spectra. Polarized reflectancespectra of pyrolusite #5 a:4.42A c:4.44A in- dicate that bands l, 2, and 4 are polarized per- a: 4.364 pendicular to the c axis and that band 3 is polarized c:2.87A b:2.87A parallel to the c axis. Band 5 is not present in the The IR spectraof this pyrolusite seriesshow con- spectra of pyrolusite #5, which is our only sample siderablevariation. The order of the spectrain Fig- with single crystalslarge enough to yield reflectance ure 3 is the same as that of the powder patterns in spectra.These results are in completeagreement with Figure 2. The spectralvariations are not well corre- the predictionsoffactor group analysisfor the tetra- lated with X-ray patterns, although two trends are gonal pyrolusite structure. Band 3 is due to the dis- suggestedin going from top to bottom in Figure 3; placementof the relative to the manga- 1202 POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES

Table L Sample information

sample 1ocallty ldent. ref. fLg. purlty cheEistry tl ll ll ll x-rav IR

Pyroluslte I Germny CIT 2853 lB pure pure Mn0, 2 Rossbach, Westphalla cIT 4511 1B pure pure 3 Lake Valley, New Mexlco CIT 2402 18 E'ram Pure 4 Nlssan, cemny HAv 93614 3 ,1B pure Pure 58 . 32 Mn : (+3 . 96) 5 Lake Valley, New Mexico HAV 111929 2 2R pure pure 5 Sierra County, New Mexlco LCM 10995 2 3 pure pure 59.52 Mni(+3.94) 7 Central New Mexlco CIT 2731 2R pure pure 8 Locality unknom CIT 9430 2R pure pure 9 Synthetic CIT 9431 3 3 pure pure 60.02 !'tn;(+3.92) 10 Synthetic CIT 9432 4 3 pure pure 50.42 Mn;(+3.98) 11 Synthetlc CIT 9433 5 3 pure pure 61.82 l'h ; (+3.99)

Nsutile 12 Nsuta, chana ctT 9434 38 PUre Mn(0,0H)..xH^0 13 Sakichateau, Belglu CIT 9196 6 n,cla 14 Hidalgo, Mexlco IIIff M-23 4 pure t,PYr 59.62 Mn;(+3.97) 15 Oxen Clain, Utah l{IilT UT-17 6 E, qrz t6 Synthetlc CIT 9435 1 5,3R pure pure L7 SyntheEic CIT 9436 8 4 pure pure 58.42 un;(+3.63) l8 Synthetlc CIT 9437 9 4,5,38 pure pure 59.52 Mni(+3.89) 19 Synthetlc CIT 9438 10 4 pure pure 58.62 Mn;(+3.89)

Ransdelllte 20 Chlhuahua, Mexlco cIT 9439 ll 7 pure Pure Mn0, 2I Black Maglc Mine, Callf. CIT 9440 48 t'hol t'hol 22 Lake Valley, New Mexlco CIT 7486 L2 48 t'pyr t,PYr Ilollandite group 23 Broken H111, N.S.W. CIT 3523 58 pure *Mn,Pb,Si Coronadl te 24 Bou Tazoutt, Morocco HI'IT MOR-5 13,14 58 pure *Mn,Pb,V ?bMn80t6 25 Inyo Co,, Callf. nAv 111927 M,qtz. *Mn,Pb,51 Cryptonelane 26 Chlhuahua, Mexico CIT 9441 13 68 !,tod pure *l'ln,K,N1,Fe KMn^0.. 27 Patagonia Mine, Arizona HWT AR-22 13 9 pure Pure *ltn,K d rb 28 Tioulne, Morocco HI''T MOR-1 t,qtz, t,qtz *l'tn,K,Ba,St'A! brn 29 l,lhtte oak Mtn., Tenn. HwT E-23 58 pure *Mn,K,A1,51,Ba 30 Synthetic CIT 9442 15 68 pure pure *Mn,K

Holland ite 31 Soharls, Sweden LCM13875 14 7R pure *Mn,Ba,K,Ca,Fe,Al,Sl BaMnr0rU 32 Synthetlc cr"t 9443 15 7R pure *lin, Ba Manj iroite 33 Synthetlc CIT 9444 15 7R pure Nt*8016

Ronanechite 34 Chihuahua, Mexlco CIT 9445 15 8B pure Pure (Psilonelane) 35 Palos Verdes H111s, Ca1lf. CIT 9446 L7 88 t,brn (Ba,Hr0)rMn.0r^ 36 Mayfield Prospect, Texas HwT, T-2 88 pure 37 Prlbble Mlne, vlrglnla H!rT' E-48 10B'8B pure 38 Van Horne, Texaa HAv 97518 18 10 pure pure Chalcophanlte group Aurorlte 39 Aurora Mlne, Nevade HST LU-21 19,20 98 t,qtz *Mn,S1,Ca,Cu,4g,Zn,K'Be (Mn,Ag,Ca)Mnr0r.3Hr0 Chalcophanite 40 Sterllng H111, NewJersey CIT 406 13,21 L2,98 pure pure ZnMnrOr.3HrO 4I Sonora, Mexlco crr 7134 98 t, qtz

Lithlophorlte 42 Postmasburg, S. Afrlca CIT 9447 22 13 Pure (A1,Li)Mn0"(OH), 43 Sausalito, Calif. CIT 7968 13,108 pure 44 Greasy Cove, Alabama HWT E-14 22 I0B pure

Blrnessite 45 Mt, st. Hilalre, Quebec CIT 8509 118 t'ser E,sel (Na,Ca,K)Mn,0,r'3H.0 46 Boron, Calif. CIT 9448 23 pure t,sll t Lq ' 47 cumington, Mass, NMNH115315 24 L4 pure t,cba? 49.4"1 Mn;(+3.70) 48 Synthetlc, K CIT 9449 25 11B pure pure 49 Synthetlc, K CIT 9450 26 14,118 pure pure 58.02 Mn; (+3.94;;*y.'X 50 Synthetic, K CIT 9451 27 14 , 11B pure Pure 48 . 82 Mn; (+3 . 90) 5L Synthetlc, Mn crr 9452 28 L4 pure *Mn 52 S)mthetlc, Na CIT 9453 26 12B pure pure *lln,!9 53 Synthetic, Ca CTT 9454 26 128 pure pure tMn,ca 54 SynEhetic, Na cIT 9455 29 14 pure pure

neseions along the direction of the octahedralchains any structural variation which may be its cause.The (by analogy with isostructuralrutile; Farner, 1974). following section on nsutite will show that the pres- It is variation in the vibration frequency of this enoe of ramsdellite double chains is not responsible movement which is responsiblefor the major varia- for the variation in the position of band 3, although it tion in the pyrolusite spectra, but it does not suggest may be responsible for the presence of band 5 and POTTER AND ROSSMAN: TETMVALENT MANGANESE OXIDES 1203

Table l. (continued)

Todorokite group 55 Palos Verdes HiIIs, Calif. cYI 9456 L7 15,138 ErSlr { Todorokite 56 Chihuahua, Mexico crr 9457 11 138 pure (Mn,Ca,Mg)Mni07.Hr0 51 Chihuahua, Mexico crr 9458 11 15 t, sll )6 Bonbay, India crr 9459 15 pure 59 Mlramati Mine, crT 9460 138 m,ngn 60 Charco Redondo, Cuba crT 9733 30 15 pure 61 Unknom locallty HWTMn-24 30 15 pure Woodrufflte 62 Sterllng H111, New Jersey NMNH114158 31 138 pure *Mn,Zn,Cu,Ca,Al (Zn,Mn)Mn^0-.H^0 Jtz

Ranclelte 63 Putonrs Cave, Virglnla NMNH120601 L7 pure Pure (Ca,Mn)Mn, 0^' 3H^0 64 Ranci€ Mtns., France NMNH128319 2T ll t,tod t, sil qt z , 32 65 Orienta Province, Cuba HAV 110334 32 17,148 n,brn m,brn 66 Itia, Greece crT 9430 33 148 PUre Buserlte 67 Synthet ic ctT 9622 34 16 pure Pure (Na, !,ln)Mnr0r.xHr0 bd Synthetlc, Co crr 9623 34 I5B pure Pure 69 Synthetlc, Mn crT 9617 34 15B m,bir, PUre lnp

1. The following abbreviations are used for saple ldentlfication numbers: CIT = Californla Institute of Technology, HAV = Harvard UnLversity, LCM = Los Angeles County ltuseun of Natural Hlstory, HWI = The Hewett Collectlon ln Possession of the U. S, Geological Survey at Denver, Colorado, NMNH= National l,luseun of Natural Hislory, The Smithsonian Inscltution; for X-ray and IR purlty M indlcates najor lnpuritles, m indicates mlnor inpurltles, t lndicates trace lnpurities. Samples are lndicated to be X-ray puredespite the presence of several weak llnes whlch do not match other standard sanples provided that these cannot be attributed to other phases. Thls was generally the case for the hollandlte group and blrnesslte. The speclal case of pyroluslte 1s dlscussed in the text' For x-ray and IR purlty the following abbrevlations are used: blr = blrnesslte, brn = braunile, cbn - carbonate, cla = clay ninerals, hol = holl.andite, inp = unidentified impurity, mgn = nanganite, pyc = pyrochrolte, pyr = pyrolusite, qLz = , ser = serandite, si1 = sillcate, tod = todoroklte. Under chemistry the nanganeae oxidation state ls enclosed l-n Darentheses. Following *, elements detected bv qualitative analysis are llsted ln apProxinate order of concentratlon; elements in trace quantlty are underlined. The chenical fomulae lncluded ln this table should be taken as only an approxlmate lndication of the chemistry of the nineral phases. The vari- allons in catlon substitution, manganese oxidatlon state, hydration, and structure preclude a slngle rlgorous chenlcal formula for many of the minerals, 2. Mislabeled as ramsdellite in the collections. 3. Synthetic nethod: McKenzie, 1971. 4, Artificial 6-Mn02i fron Natlonal Carbon Company. 5. HP; fron DLanond Shamrock Chenical Companv, Baltimore, Maryland; 99.9"A|ftiO2,0.0052 Fe by thelr analysis. 6, zwicker et ar., 1962. 7. Synthetic nethod: preparatlon a for q" - Mnor from Gattow and Glenser, 1961a. 8' Synthetic method: electrolytic preparation fir n - Mn02 from cattow and Glenser, 196Ia. 9. Synthetic nethod: Giovanoli et al., 1967. 10. Synthetic method; clovanoli et a1., 1967, IO.O N HNO3was used in place of 1.0 N HNO3. 11. Finkelman et al.. ).974, L2. Apparently a poor sanple of Lake Valley ransdelllte since the ransdelllte structure was detemlned on naterial from Lake Valtey. 13, palanche er a1., 1944. 14. Bysrrijm and Bysrr6n, 1950. 15. S)mthetic nethod: preparation //1, McKenzie, 1971; Ba(MnOq)2 and NaMnO4were used in place of KMn04 for synthesis of hollandite and mnjiroite respectively. 16. The locality is described in Flnkelman et aL,, 1974. 17. The locallty is descrlbed in Mirchel ani-C6:rey, 1973. 18, Fleischer, 1960 19. Radtke et al.,1967. 20. Plior to analysis major tnpurity was removed by 10 ninute treatment wlth dllute acetlc acid followed by washing wlth deionized water: 2L. Wadsley, 1955. 22. Fleischer and Faust, 1962. 23. Brom er al., 1971. 24. Frondel et aI., 1960a. 25. Synthetlc nethod: The first preparation for 6-MnO2 from Glenser et al., 1951. 26' Synthetic nelhod: preparatlon /11, McKenzie, 1971; Ca(MnOa)2 and NallnOq were used in place of KMn04 for synthesls of Ca and Na birnessites. Synthesis nethod: as for preparation /,l8 (Buser et al., Table 4) but noles HCl = 0.125; from Buser et al., 1954. 28. Synthetic nethod: nanganese(Ill) manganate (IV) uas prepared according to Giovanoll et al., 1970b, and was dried 10 hours at room temperature under approximately IO-5 torr. 29. Syntbetic method: Na mrnganese(II,III) nanganate(IV) was prepared according to ciovanol-i et al., 1970a, but was not dried' The solid from OoC oxidatlon vas washed by filtration and kept under deionized water. 30. Frondel ec al. ' 1960b. 31. Frondel, 1953. 32. Richnond, 1969. 33. Bardossy and BrindLey, 1978. 34. Synthetic method: buserite was prepared by the method of Glovanoli (1970a) for Na manganese(II,IIf) nanganate(IV). The oxidation product was washed wlth deionized water and stored as an aqueous suspenslon. Co and l,ln analogs were prepared by the nethod of MeKenzie. 197I. the variation in the position of band 4. Manganese proven orthorhombic modification, detailed struc- oxidation state(Table l) is not correlatedto the posi- tural work on pyrolusite singlecrystals is warranted. tion of band 3. The positions and relative intensities of bands I In light of this unexplained variation in pyrolusite and 2 uniquely and clearly distinguish pyrolusite IR spectra, the unindexed X-ray lines, and the from the other manganeseoxides. POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES

trum clearly distinguishesit from all other manga- nese oxides except the hollandite group and some synthetic nsutites. The presenceof band 7 and the position of band 2 distinguish ramsdellite from the pyrolusile hollandite group. The presenceof band 7 distin- guishesit from nsutite. pyrolus ite E Nsutite Nsutite is a structural intergrowth of pyrolusite romsdellite and ramsdellitein which layers of single and double E chains alternate in random fashion (de Wol-ff, 1959; Laudy and de Wolff, 1963).One of the many possible structural variations is shown in Figure l. Natural Fig. l. chain structures, looking nsutites exhibit a range of X-ray dif- approximatelydown c (modified from Clark, 1972,p.228,237). and synthetic fraction patterns which have been interpreted to be the result of variation in the concentrationof pyrolu- Ramsdellite site microdomains.The changesin X-ray line sharp- Ramsdellitehas a chain structuresimilar to that of ness,number, and position for the nsutite patternsin pyrolusite. In ramsdellitethe chains are doubled by Figure 2 arcin agreementwith that expectedin going the sharing of edgesbetween two adjacent chains; from a low (#18) to a high (#17) concentrationof these double chains are linked by shared vertices pyrolusite microdomains(de Wolff, 1959;Laudy and (Bystrom,1949). de Wolff, 1963).Heat-treatment of nsutite producesa Ramsdellitehas been thought to be the only other seriesof materialscontinuing this transition in X-ray stoichiometricmanganese dioxide besidespyrolusite. powder pattern to that of a disordered pyrolusite We have found that it invariably contains a single (Gattow and Glemser, l96la; Brenet et al., 1958). crystallographically-orderedwater. The IR spectrum These are thought to be a continuation of the struc- of ramsdellite is shown in Figure 4. Although we tural seriespostulated for unheated samples(Laudy were able to obtain only one pure ramsdellite, and de Woltr, 1963). spectraof three others were identical to Figure 4 in Our work supportsthe conclusionof Laudy and de band number and position and with only minor vari- Wolff that progressiveheat-treatment of nsutite pro- ation in band intensity when absorption due to the ducesincreasing concentrations of randomly distrib- impurities was subtracted. Bands 8, 9, and l0 are uted pyrolusite microdomains, but it suggeststhat present in the spectra of all ramsdellites listed in variations in unheated samples are predominantly Table I and are also presentin pyrolusite #3, which the result of differencesin crystalline order. We have contains ramsdellite impurity. Band 8 is due to an progressivelyheated two nsutites and in each case HrO bending vibration. The intensity relationshipof the bands indicate that the major hydrous speciesis HrO; the sharpnessof band l0 and the structure on . ,' H . band 8 indicates that the water is in a well-defined ; crystallographic site. The ramsdellite structure was determinedfor a samplecontaining 1.3percent water @ystrom, 1949),which is characteristicof other rams- dellite samples (Fleischer et al., 1962). This water was assumedto be an impurity. The presenceof a crystallographically well-ordered water in all our ramsdellite samplessuggests that it may be an in- tegral part of the structure.The intensitiesof the wa- ter bandsare approximatelythe sameas thosefor the hydrousmanganese oxide romanechite(Fig. l0). The analyses in Fleischer et al. indicate a stoichiometry Fig. 2. X-ray powder diffraction patternsof the chain-structure MnO,'0.06H,O. manganeseoxides, showing an increasing degree of orthorhombic The overall character of the ramsdellite IR spec- distortion for pyrolusite. POTTER AND ROSSMAN:TE7:RAVALENT MANGANESE OXIDES I2O5

NRVELENGTH(HrcBoNs) reflects differencesin the crystalline order of the sam- 8l0ls25 ples. The decreasein sharpnessand nu'r,ber of X-ray lines, which has commonly been interpreted as in- PYBOLUSITES dicating a high concentration of pyrolusite micro- domains, appears to be primarily indicative of dis- order. We have no explanation for the variation in relative intensity of the absorption bands.The band intensity relationship for each nsutite is maintained through the heat-inducedtransformation to pyrolu- -] site and is therefore unrelated to the concentration of ol pyrolusite microdomains.It appearsto be related to variation position pyrolusite u.J the in the of band 3, al- (J z. though it should be noted that pyrolusite band 3 has CE 6 developedfrom different nsutite bands in Figures 5 Ctr cl and 6. a CD All nsutites have a broad absorption in the 3600 CE cm-' to 3100cm-' region. This is generallyof low in- tensity but becomesmore intense with decreasein crystalline order. [t is attributable primarily to water in the more disorderedcases, but may be either water or hydroxyl in those sampleswith a higher degreeof ENNONUHBER543 order. ENNOFOSITION T II Nsutite #14 in Figure 7 is characteristicof the nat- 1200 1000 800 600 q00 ural sampleswe have studied. Natural processesat I,,lFVENUMBER Fig. 3. IR.spectra of pyrolusites.Presentation intensities: #ll. NRVELENGTH 16l%o:#9, ll2Vo;#6, l43%o;#10, l2Vo; #4, l27%o. 3q56 (r'II ol obtained a seriesof X-ray patternssimilar to that of I BRMSDELLITE Brenet et al. Both exhibit variations in band position 20 l! and intensity (Fig. 5 and 6) which cannot be repro- (J z. duced by addition of various proportions of pyrolu- CE co site and nsutite spectra.They are thereforenot phys- cc O ltl ical mixtures of pyrolusite and nsutite, and Figures 5 a m il ro9 and 6 indicate the effecton the IR spectrumof varia- CE tion in the concentrationof pyrolusite microdomains. s600 3000 2q00 1800 The spectrapresented in Figure 7 span the range of NFVENUMBEB variation for unheatedsynthetic and natural nsutites. NRVELENGTH

[^IRVELENGTH bandssuggest that little is presentand that it doesnot well-definedcrystallographic sites. Fig. 5. The effect of progressiveheat-treatment on the IR occupy spectrum of nsutite #16. Presentationintensities: 48O"C, l37%o; The spectraof our samplesdo not show a continu- 32O"C, l20%o;21 O" C, l06vo;35" C, 1059o. ous variation between hollandite and romanechite theselocalities apparentlyproduce nsutites of similar NRVELENGTH(iltcnoNs) crystalline order and concentration of pyrolusite mi- 8101525 crodomains. The positionsof bands I and 5 (Fig. 7) distinguish HERT-TRERTED natural nsutites from the hollandite group, whose NSUTI TE spectra are similar. Synthetic nsutites which have spectra close to that of ramsdellite can be distin- guished from it by band 5, which is a single band in nsutite and split in ramsdellite,and by the absenceof J ramsdellitebands 8 and 9. q group The channel structures: the hollandite and lrl romanechite () z CE (D (E The hollandite group o (t) (D The structure of the hollandite-group minerals CE (Figure 8) consistsof MnOu octahedrawhich share edgesto form double chains as in ramsdellite (By- strtjm and Bystrdm, 1950,1951). These double chains are linked by shared verticesforming channels;Ba, K, Pb, or Na are presentin the channelsand coordi- nated to the oxygensof the double chains.The iden- the mineral tity of the channel cations determines 1200 1000 800 600 q00 species. !.IFVENUMBEB IR spectroscopyin the 1400cm-'-200 cm-' region Fig. 6. The effect of progressive heat-treatment on the IR does not distinguish among the various minerals in spectrum of nsutite #18. Presentation intensities: 480"C, 62Vo; the hollandite group; the spectrum in Figure 9 is rep- 320o C, 47 Vo; 225" C, 66Vo; 35" C, 8Ma POTTER AND ROSSMAN:TETRAVALENT MANGANESE OXIDES l2u

]^IRVELENGTH

NRVELENGTH and relative intensities are in good agreement with 810152s Mukherjee'ssample. Figure l0 is representativeof the spectraof all the romanechitesof Table l. There is negligiblevariation d CBYPTOMELRNE in band position and, with the exceptionof band 4, in HOLLRNOITEGffOUP band intensity. Figure l0 shows the maxi- ltl relative (J for band 4. In some z mum relative intensity observed CE it is presentonly as a prominent shoulder. m instances (tr present in romanechite (tr 27 The same major bands are a as in the nsutites. ramsdellite. and the hollandite 6 5 432 CE group, but the relative intensitiesdiffer. For romane- 1200 1000 800 600 tl00 chite, band 7 is invariably a weak shoulder,band 6 a NRVENUMBEB major band. In addition, bands 3 and 4 are peculiar Fig. 9. IR spectrumof cryptomelane,which is representativeof to romanechite.Bands I and 2 are diagnosticof ro- the hollandite group. Presentationintensity: 1337o. manechite, although the latter is so weak as to be missed in poorly crystalline samples.The positions and sharpnessofbands 9, 10, and ll are diagnostic ter, but is more likely an artifact due to the Christian- of romanechite and are clearly recognizable in most sen effect (Prost, 1973),a result of samples. mismatch between TlBr and the sample. The IR spectrumshows no evidencefor hydroxide ions. The The layer structures:chalcophanite, aurorite, and intensity of the water bands varies from sample to lithiophorite sample,indicatin8 a variable water content in accord and aurorite with the chemical data of Fleischer (1960)for other Chalcophanite romanechites. These results are in accord with the The chalcophanite structure (Wadsley, 1955) is formula of Wadsley, in which the hydrous com- basedon layersof edge-shared,MnO.octahedra (Fig. ponent is water, and inconsistentwith that of Muk- ll). One out of sevenoctahedral sites in the MnO" herjee, in which hydrogen is present as hydroxide layer is vacant. These alternate with layers of zinc ion. Thesewater IR featuresare characteristicof all and layers of water in the stackingsequence: Mn-O- the romanechiteslisted in Table I with the exception Zn-HrO-Zn-O-Mn. All waters are thought to be of #35, which has negligible absorption due to hy- structurally equivalent,with weak hydrogen-bonding drous components.It thus appearsthat water rather betweenwater molecules.Our work supportsWads- than hydroxide ion is characteristic of romanechite. ley's inferencesregarding the nature of the hydrous Our evidence suggeststhat our samplesare analo- component.Bands ll, 12,and 13 are characteristicof gous to that of Mukherjee. Both sampleswhich were water in a single, crystallographically-orderedsite. X-rayed gave powder patterns whose line positions The band position indicatesapproximately the same

hIFVELENGTH I^IFVENUMBEB

to those of chalcophanite but with all octahedral sites filled. These layers alternate with layers of (Al,LiXOH)o octahedra.There is no ordering of the Al and Li in these octahedral sites. Wadsley sug- gestedthat hydrogen bonding exists betweenlayers and that the hydroxide ions are aligned per- pendicularto the layers. Our work gsnfirms Wadsley'ssuggestions regard- ing the nature of the hydrous component. The single, sharp, absorptionband near 3400cm-' togetherwith the nearly complete absenceof the water bending mode near 1600 cm-' in the spectrum of #42 (Fig. b 13) indicates11p1a single type of hydroxide ion pre- dominates. In addition, in the well-crystallized \--o samplethere are two weak shoulderson the low-en- Fig. ll. ChalcophaniteMnO5, layer structure,the aD plane. ergy side of band I I which are resolvedat liquid ni- trogen temperature.Single-crystal, polarized IR re- flectance work shows that all three bands are degreeof hydrogen-bondingas in liquid water. The polarized perpendicular to the basal . The IR spectrum of the other chalcophanite in Table I ions are thus aligned in this direction. The matchesFigure 12 exactly exceptfor minor variation hydroxide in relative band intensity. lower-intensity bands may oorrespondto hydroxide in local environments created by statistically less X-ray powder diffraction patterns indicate that probable populations of Al and Li atoms in nearby aurorite has the chalcophanitestructure (Radtke et sites. al., 1967).We have confirmed this. The absorption octahedral from bands in the IR spectrum are identical in number Lithiophorite can be distinguished all other manganeseoxides by the intensity and position of and position to thoseof chalcophanitealthough there band I I and by the presenceofband 9. The positions are somedifferences in relative intensity. of all the bands in the intensity relationship of Figure The position and sharpnessof bands 12 and 13 13 are also diagnostic of lithiophorite. Both well- and the sequenceof four bands in the 550 cm-' to (#42) and poorly-crystallized(#43) sam- 4@ cm-' region distinguish chalcophaniteand auro- crystallized ples rite from all other manganeseoxides. are shown. Incompletely characterized structures: birnessite, Lithiophorite todorokite, buserite, woodruffite, and rancieite The structure of lithiophorite (Wadsley, 1952) Considerableconfusion exists with respectto the consistsof layers of edge-sharedoctahedra similar structural natures and relationships of the materials

NRVELENGTH 3'l 5 NRVELENGTH hIRVENUMBER Fig. 12. IR spectrumofchalcophanite. Presentationintensity: 16l%. 1210 POTTER AND ROSSMAN:TETRAVALENT MANGANESE OXIDES

NRVELENGTH 3tl 5 8101525

LI THI OPHOBITES L I THI OPHORITES cil",l d J lrl lrl (J (J z. z 43 CE CE 43 co CD (t E. O o a a cct 42 (D CE CE 42 9 8 76 54321 1200 1000 800 600 q00 3600 3000 2q00 1800 hIRVENUMBEB I,,IFVENUMBEBccx-l > Fig. 13. IR spectraoflithiophorites. Presentationintensities: #43, l72Vo;#42, l73%o. consideredin this section.This is a direct result of the basic structures.The one exceptionis #54. Most of poor responseof X-ray diffraction to their minute its bands are shifted by 2040 cm-' from those of particle sizes,poor crystalline order, and structural other samples,and it differs from all othersin the ab- variations within a mineral group. The natural sam- senceof band 7 and the splitting of band 4.' The ples we have examined indicate that birnessite,to- sharpnessof its bands indicates that it has a higher dorokite, and rancieite, when well-crystallized, are degree of order than the other samples.Structural structurally distinct from one another. With increas- changesrelating to this ordering could be responsible ing disorder, however, the structural distinctions for the band shifts. We have classedsample #54 as a among them become more subtle or vanish alto- structural variant of the birnessitegroup but we do gether.We feel that the structural differencesamong not feel that the data are compelling evidence for thesethree merit their considerationas distinct min- this. eral phases and have consequentlyorganized this The basic structure of the birnessite group has section with a subsection for each. The synthetic been inferred from the postulated structuresof so- phasebuserite may be related to birnessitebut is in- dium manganese(Il,Ill) manganate(IV) (our birnes- cluded in a separatesubsection to facilitate dis- site #54) and manganese(Il! manganate(IV) (our cussion. birnessite#51) (Giovanoli et al.,l970a,b). Although there is somequestion of the validity of the former as Birnessite a syntheticbirnessite, the latter is clearly a represen- Giovanoli (1969) has suggestedthat birnessiteoc- tative of the group as a whole. The proposedstruc- curs in an infinity of structural varietiesall basedon ture is similar to that of chalcophanite.MnOu octahe- the samecrystal lattice but difering in crystallite size, dral layers have a vacancy in one out of every six lattice order, manganeseoxidation state, and cation octahedral sites. These are separatedby layers of substitution.Our work supportsthis view. IR spectra lower-valent cations and by layers of water and hy- of both natural and syntheticbirnessites show varia- droxide ions. Our work has several implications tion in band position and, to a larger extent, relative which support this structure. The positions of the band intensity (Fig. l4). Suchvariations do not occur major bandsin the 1400cm-' to 200 cm-r region sug- for those manganeseoxides with a single, well-de- gest that birnessiteshave a layer structure, as dis- fined structure, but are characteristic of the structur- cussedin a later section.The fact that the identity of ally-variable nsutite. Nevertheless,the general simi- larity of the spectra strongly suggeststhat most a The higher wavenumber component of band 4, sample #54, birnessite samples are characterized by the same may actually correlate to band 5. POTTER AND ROSSMAN: TETMVALENT MANGANESE OXIDES t2tl

NRVELENGTH 3rl 5 hIRVELENGTH(HrcBoNS) 8101525 BIBNESSI TES BI BNESSITES

-t (?rlI ol J -] dl (-)UJ z- r! (J co z. cc CE O m a G co O CE rD CE

---=----_J-. lll iltog I BFNONUHtsEB 7 ERNOPOSITION I 3600 3000 21100 1800 1200 1000 800 600 rl00 HRVENUMBER I,IflVENUMBEB

Fig. 14.IR spectraof birnessites.Presentation intensities: #50, 1069o;#47, 247Va;#51, 99Vo;#49, lMVo;#54, 53Vo

the large cations doesnot influence thesebands sug- may be difficult to distinguish from highly disordered geststhat the cations are weakly bound to the MnOu todorokite. octahedrallayers. We interpret the 4000cm-' to 1400 cm-' pattern as follows: a hydroxide ion in a specific Birnessite vs. vernadite (6-MnOr) crystallographicsite produces band 10, and a less- 6-MnOr, also called vernadite, is a hydrous, ordered water producesthe remaining features. slightly crystalline material which usually shows only The spectrain Figure 14 are anangedin order of two X-ray diffraction lines at 1.4 and 2.4A. Because, increasingband sharpness,which reflectscrystalline in part, these are two of the strongest birnessite lines, order. In general,X-ray powder patterns do not fol- Giovanoli (1969) considered &-MnO, and birnessite low this trend. This suggeststhe presencein some to be two members of a single group. Giovanoli et al. samplesof a disorderedcomponent to which X-ray (1973) suggest that members of the birnessite group diffraction is insensitive. show a continuum of variation in crystalline order. Natural birnessite is distinguished from most of On the basis of electron diffraction, Chukhrov et a/. the manganeseoxides by the presenceofbands 3 and (1978a, b) concluded that birnessite and vernadite 4 as two broad features.It can be distinguishedfrom have different c parameters and are appropriately poorly-orderedchalcophanite and generallyfrom to- considered different mineral species. dorokite by the features in the 4000 cm-' to 1400 Chukhrov et al. presetted IR spectra of a birnes- cm-' region.It can be distinguishedfrom rancieiteby site and several vernadites and concluded that differ- the position of band 7 near 750 cm-', by the absence ences in the IR pattern of the two materials sup- of rancieite band 4 near 700 cm-', and generally by ported their conclusion that they are diferent the relative intensity and positionsof the two major mineral species. Their birnessite had prominent bands. Synthetic birnessitecan be distinguishedby bands at 510 and 47O cm-' whereas the best verna- these criteria and, for well-ordered material, by the dite pattern had the corresponding bands at 500 and general character of the spectrum. Some samples 435 cm-'. We note that both of the bands in both ma- tzl2 POTTERAND ROSSMAN: TETRAVALENT MANGANESE OXIDES terials fall within the rangeof variation in the spectra NRVELENGTH aqueoussuspension matched that reported by Wad- Fig. 15. IR spectraof buserite.The top spectrumwas obtained sley (1950a).Its IR spectrum(Fig. 15) was obtained by the petroleumjelly mull techniquedescribed in the text. The was obtained by the wet TlBr pellet technique in two ways. First, a TlBr pellet was preparedin the middle spectrum described in the text, presentation intensity: 72Vo.Thc bottom usual way exceptthat the samplewas added to pow- spectrum was obtained normally, presentation intensily: 97Vo. dered TlBr as a thick water slurry and the pellet was not pressedunder vacuum. The resulting pellet was erite spectrum with that of its dehydration product, surroundedby water as it camefrom the press,and a sodium manganese(Il,Ill) manganate(IV) (Fig. 14, high concentration of liquid water is shown to be #54) indicates that no significant structural rear- presentwithin the pellet by the intensity of the HrO rangement of the manganeseoctahedral framework stretch and bending bands near 3400 cm-' and 1600 has occurred during dehydration. The close similar- cm-' (not shown) and the broad vibrational bands in ity of the spectra of cation-exchangedbuserites to the 600 cm-' to 850cm-' region (Fig. l5). We believe that of sodium buserite supports those conclusions. that the buseritein the TlBr pellet hasnot been dehy- The materials do not dehydrateso readily as sodium drated, but we are unable to show this by X-ray dif- buserite and can be air-dried without losing the l0A fraction due to its low concentration in the TlBr. spacing. We have found that the spectra of both Therefore we obtained the spectrumof buseritein a manganese and buserites di,ffer from that of petroleum jelly mull. Buserite in water suspension sodium buserite only in the sharpnessof the bands, was dropped onto filter paper.When the excesswater which reflects crystalline order. Giovanob et al. was removedby the capillary action of the paper,the (1975)have concludedthat the l0A manganeseoxide resultingpaste was mixed with petroleumjelly, sand- phasesare hydratesofthe 7A phases.Insofar as bus- wiched betweentwo TlBr platesand run vs. a petro- erite and sodium manganese(Il,Ill) manganate(IV) leum jelly-TlBr blank. SubsequentX-ray diffraction are concerned,our work supportsthis. of the mull showed that no dehydration had oc- Well-crystallizedbuserite 15 dislinguished from all curred. The l0A line remained without a trace of a other manganeseoxides except sodium manga- 7A line, although there was some alteration of the nese(II,IIf manganate(Iv) by the positionsand rela- relative intensitiesof the other lines. The spectrumof tive intensitiesof its IR featuresin the 1400cm-' to sodium buserite from this mull technique (Fig. 15) 200 cm-' region. When highly disordered it may be has considerableabsorption from liquid water in the difficult to tell from some birnessites and from 800 cm-' to 600 cm-' region. Comparisonof the bus- highly-disorderedtodorokite. POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES t2t3

Todorokite and woodruffie not show evidence for manganite, although as little as 57ocould be recognizedfrom the sharp -hy- The validity of todorokite as a single mineral droxide bands near ll00 cm-' and the hydroxyl phase has been questioned (Giovanoli et al., l97l; bands near 27OOcm-' and 2100 cm-' (Fig. 4A). No Giovanoli and Btirki, 1975).On the basisof electron combination of the bands of other manganeseoxides microscopy and electron diffraction, they concluded can duplicate the water-hydroxide ion bands of the that it is a mixture of buseriteand the products of its todorokite spectrum. Such a characteristicIR spec- dehydration (birnessite)and reduction (manganite). trum with complex featuresnot attributable to other None of the todorokite sampleswe have examined known phasesis strong evidencefor a specific,char- can be such a mixture; our work strongly suggests acteristicstructure. that todorokite is a valid mineral species.The varia- Comparisonof the buseriteand todorokite spectra tion in todorokite IR spectra (Fig. 16) is pre- show that buserite is not a todorokite analog. The dominantly one of crystalline order. There is little water and hydroxide bandsof the two materialshave variation in band position, and the spectrumof even no similarity, and there is no correspondencebe- the most disorderedmaterial retainsindications of all tweenmost of the bandsin the 1400cm-' to 200 cm-' but the most minor bandsof the well-crystallizedma- region unlessthey are shifted up to 40 cm-r. Natural terial. The large variation in relative band intensities todorokites do not show such large band shifts. Syn- expectedfor a mixture of phasesis absentin the 1400 thetic todorokites prepared by cation exchange of cm-'to 2@ cm-'region. The variationin intensityof buserite (McKenzie, l97l) are incorrectly named. bands 16 and 17 is due to an increasingratio of ab- The structure of todorokite is not known. Crystal sorbedwater to crystallographicwater with decreas- morphology and cleavagesuggest that todorokite has ing crystalline order. a channel structure similar to hollandite or romane- The spectrum characteristicof todorokite cannot chite (Burns and Burns, 1975, 197'7a,b). Our work be produced by the addition of the spectraof bus- suggeststhat it has a layer structure.This will be con- erite, birnessite,and manganite.Our todorokites do sidered in detail in a later section. Our work also

NRVELENGTH(ilrcnoNs) hIRVELENGTH

TODOBOKI TES

olrl J

ttJ (J UJ CJ z. z. cf CE (D co (E cc o O an (t) (D 6 CE CE

1817t6 t5 t4t2 lf lo9 653 2l 3600 3000 21100 1800 1200 1000 800 600 q00 hIFVENUMBEB I,IRVENUMBEB

NRVELENGTH

-t RRNCIEITES RFNCIEITES (r)l cil I -l c)l.l ol IJJ I (J z. CE ul 65 co (-) cc z. O CE a co co (E cf c) 64 a (D CE 3600 s000 2q00 1800 I,'IFVENUMBEB 63 43 2l 1200 1000 800 600 q00 I^IRVENUMBEB

those of some birnessites,but other rancieite spectra (Fig. 17, #63) differ significantly. Those rancieite * samples with the most distinctive IR patterns are e o those for which the characteristic rancieite softness o and color (Palacheet p. al., 1944, 572;Richmond et E al., 1969\are most apparent.The structural implica- tion of the rancieite spectrawill be consideredmore fully in the next section. Most rancieite samplescan be distinguishedfrom other manganeseoxides by the high relative intensity of the band l. Some samplescan easily be confused E with disordered c todorokite or birnessite; however, o rancieite band 4 at 680 cm-' distinguishes rancieite o

from theseother two, which absorb at760 cm-' and E 750 cm-' respectively. o

o Generalrelations of infrared spectrato structure E The IR spectraof the manganeseoxides, except for lithiophorite, are dependent only on the MnOu oc- tahedral framework. If bands in the spectraare the result of vibrations in which the large cationspartici- pate significantly, then changesin the mass of these edgesshored per MnOaoclohedron cations should be reflectedin the spectra.However, substitution in the hollandite group and the birnes- Fig. 18. Correlation of octahedral polymerization with major IR positions. sitesleaves the spectrain the mid-infrared region un- band Dot size approximately proportional to band changed. intensity. Intense absorption band positions define a trend which Neither could the effect of cation sub- relates to octahedral edge-sharing. stitution be seenfor chalcophaniteand aurorite and for todorokite and woodruffite, although the extent of the changeis lesssince it involves incompletesub- plotted vs. their averageMnOu octahedralpolymeri- stitution involving elements of relatively similar zation. A trend is observed showing a general de- mass.Therefore we conclude that the large cations creasein band energywith increasingoctahedral po- are not involved in the bands in this region of lymerization. The point for manganosite(Fig. 5A) is spectra. Only for lithiophorite, where light atoms included as well.u This trend can be used in con- other than manganeseform a major part of the crys- junction with a direct comparisonof IR patterns to tal structure,are bands in the 1400cm-' to 200 cm-, infer unknown structures.The positions of the low- region clearly attributable to other cations. Lith- energy bands ofbirnessite support its proposedlayer iophorite bands near 1000 cm-' and 900 cm-' are structure (Giovanoli et al., 1970a, b), which placesit probably due to (AI,LD-OH. The reasonfor this in- at 4.8 sharededges per octahedron. sensitivity may be that the bands are relatively weak The spectraof todorokite suggestthat its structure and therefore absorb at lower energies.Hollandite is based on MnOu octahedral layers. The positions and cryptomelanespectra difer in the 200 cm-' to 30 and intensitiesof the major bands of todorokite sam- cm-' region, and the difference may be due to the ples with the highest crystalline order suggesta po- identity of the channel cations. An alternative ex- lymerization near 5 shared edges per octahedron. planation is that the large cations are at too low a This is consistent with a highly polymerized chain or concentration in the structures to give observable bands. Although mid-infrared spectroscopyis in- 6 Manganosite,MnO, has the NaCl structure. Being a Mn2+ sensitive to the ihannel and interlayer cations, it is mineral it is not strictly applicable to a trend involving pre- diagnosticof the structural group. dominantly Mna+ minerals; however, the similarity in the posi- The spectraprovide someindication of the polym- tions of the low-energybands of ramsdelliteand groutitc (Fig. 7, Fig. 2A), which have erization by edge-sharingof the MnO6 octahedrain analogousstnrctur€s (Bystrdm, 1949;Dent Glasserand Ingram, 1968)and differ in oxidation manganeseoxides. state,suggests In Fig. 18the positionsof the ma- that structure rather than oxidation state is the dominant factor in jor bands of thoseminerals with known structureare determining band position. t2t6 POTT:ERAND ROSSMAN: TETRAVALENT MANGANESE OXIDES channel structureand with a layer structurecontain- as evidence for a structural continuum from well- ing some vacancies.In order to attain a polymeriza- crystallized birnessite (Fig. 14, #54) to well-crystal- tion of 5 shared edgesper octahedronin a chain or lized rancieite (Fig. 17, #63).In this case the smooth channel structure it is necessaryto build them from change in relative intensity and position of rancieite units whose averagepolymerization is 5. This corre- band I (Fig. 17) would reflect the degree of birnessite sponds to quadruple chains. No chain or channel "character." manganeseoxides composedof such large units are The lower valent manganese oxides known to exist, although isolated quadruple chains have been observedin hollandite in electron micro- We have included as Appendix A spectra of well- scopeimages (Turner and Buseck, 1979).It appears characterned samples of the following lower valent that for highly polymerized structuresa layer struc- manganese oxides: braunite, groutite, , ture is preferred. Direct comparison of todorokite manganite, manganosite, partridgeite and quense- spectrato those of other manganeseoxides supports lite.3 In some cases these are necessary for the inter- this. All known layer structureshave a strongband in pretation of the earlier sections of the paper. Others the 400 cm-' to 450 cm-' region, which is analogous are included so that this paper may serve as a com- to todorokite band 4 at 430 cm-'. Strong absorption pilation of the spectra of all manganese oxides com- in this region doesnot occur for the chain and chan- monly encountered in nature. They illustrate the nel structures.These suggestionscontrast with pre- ability of infrared spectroscopy to produce patterns vious work which suggeststhat todorokite has a diagnostic for each mineral phase for the whole channel structure (Burns and Burns, 1977a).This range of naturally occurring manganese oxides. It ex- was basedon the needle-likemorphology of todoro- tends the usefulness ofthis paper as a data base for kite and the presenceof two perfect cleavageplanes further structural work on the manganese oxide. seenunder the electron microscope.Todorokite oc- Conclusions curs in other morphologiesas well. Todorokite #58 has a platy morphology reminiscent of birnessite. Infrared spectroscopy has proven to be a useful Weissenbergsingle-crystal X-ray diffraction indicates tool for the mineralogical identification of the tet- that the sample is ordered in the same plane as the ravalent manganese oxides. Different oxides can be plates but disordered in planes perpendicular to distinguished by absorption patterns due to vibra- them. This suggeststhat it consistsof a random su- tions of the MnOu octahedral framwork in the 1400 perposition of single-crystal todorokite plates and cm-' to 200 cm-' region. The 4000 cm-'to 1400 cm-' eliminates the possibility that it is a massof needles region is often diagnostic due to absorption associ- that appear morphologically as a plate. ated with the hydrous components of the oxides. The spectra of rancieite suggesta polymerization Because of its sensitivity to short range order, in- near 6 shared edges per octahedron, which corre- frared spectroscopy gives more reliable information spondsto a filled octahedrallayer. than X-ray diffraction when applied to disordered Spectra of samplesof birnessite,todorokite, and and finely particulate samples. With X-ray diffrac- rancieitemay be similar in the 1400cm-' to 200 cm-' tion a small amount of well-crystallized material in a region. For birnessiteand todorokite this similarity is disordered or finely particulate matrix can give the related to crystalline disorder. For the most dis- impression that the whole sample is well-crystallized. ordered birnessiteand todorokite, the IR spectraare The lack of correspondence between the degree of similar(e.g.,#50 and #57).Interestingly,because the order indicated by these two techniques for our bir- X-ray order doesnot necessarilyfollow the IR order, nessite samples as a manifestation of this effect. X- sample #57 is readily identified as todorokite from ray diffraction data alone could to an error in the X-ray pattern, whereassample #50 has a diffuse mineralogical identification of the disordered mate- X-ray pattern, barely recognizableas birnessite.As rial if a well-crystallized minor component of differ- the order increases,the spectraof the two minerals ent mineralogy is present. For minerals which have become more distinct from one another. This sug- only a few characteristic X-ray diffraction lines, such geststhat birnessiteand todorokite are built of fun- as birnessite, todorokite, and rancieite, infrared spec- damentally similar units and that it is the ordering of troscopy has shown that X-ray diffraction alone may these units which makes the minerals distinct from be an insufficient test for the validity of synthetic an- one another.We believethat this is the casefor ran- alogs. cieite as well, but our data could also be interpreted IR spectroscopy can also contribute to the determi- POTTER AND ROSSMAN: TETRAVALENT MANGANESE OXIDES 12t7

nation of the structuresand structural relationships Bystrdm, A. and A. M. Bystrcim(1950) The of among the tetravalent manganeseoxides. We have hollandite, the related manganeseoxide minerals,and a-MnOr. been able to suggestfeatures of the unknown oxide Acta Crystallogr.,3, 146-154. _ _ (1951) positions structuresbased and The of the barium atoms in on their IR spectraand the relation hollandite. Acta Crystallogr.,4, 469. of these spectrato those of manganeseoxides with Champness,P. E. (1971) The transformation manganite + py- known structure. We have applied IR spectroscopy rolusite. M ineral. Mag., 38,245-248. to the role of water and hydroxide ion, whose pres- Chukrov, F. V., A. I. Gorshkov, E. S. Rudnitskaya,V. V. Ber- ence and structural orientationscan only be inferred ezovskayaand A. V. Sivtsov(1978a) On vernadite.(in Russian) Izvest.Akad. Nark. from X-ray SSS& Ser. Geol.,5-19. and chemical data. E. S. Rudnitskayaand A. V. Sivtsov(1978b) The charac- Now that IR spectraof well-charactet'aedmanga- teristics of birnessite.(in Russian) Izvest.Akad. Naz&. SSSR, nese oxide samplesare available to serve as stan- Ser.Geol.,67-'16. dards, this technique should find wider application Clark, G. M. (1972) The Structuresof Non-molecalar Solids:A for mineralogical identification of manganese Coordinated Polyhedron Approach. Applied SciencePublishers, oxides London. in the terrestrial and aquatic environments. Cole, W. F., A. D. Wadsleyand A. Walkley (1947)An X-ray dif- fraction study of manganesedioxide. Trans. Electrochem. Soc., Acknowledgments 92, 133-158. We thank the following for providing samplesfor this study: de WolS P. M. (1959)Interpretation of some7-MnO2 diffraction patterns. J. S. White, Jr., SmithsonianInstitution; C. G. Cunningham,U. S. Acta Crystallogr.,I 2, 341-345. Dent Glasser,L. S. and L. Ingram (1968)Refinement of the crys- GeologicalSurvey; A. R. Kampf, Los AngelesCounty Museum of structure groutite, Natural History; R. G. Burns and V. M. Burns, MassachusettsIn- tal of a-MnOOH. Acta Crystallogr.,24, 1233- stitute of Technology;A. J. Bauman, Jet propulsion Laboratory; 1236. G. W. Brindley, PennsylvaniaState University; A. S. Corey, pasa- Farmer, V. C. (Ed.) (1974) TheInfrared Spectraof Minerals.Min- dena City College; V. Morgan, Boron, California; L. Dalbec, eral Societyof London, London. Ridgecrest, California; and R. Currier, Arcadia, California. A Finkelman, R. 8., H. T. Evans,Jr. and J. J. Matzdo (1974)Man- geodes small portion of the funding for this work was provided by the ganeseminerals in from Chihuahua, Mexico. Mineral. L. S. B. Leakey Foundation and the John A. McCarthy Founda- Mag., 39,549-558. M. (1960) tion. Helpful critical reviewswere provided by R. G. Burns and R. Fleischer, Studiesof the manganeseoxide minerals.III. Giovanoli, Berne. Psilomelane.Am. Mineral., 45, l'16-18'1. - and G. T. Faust (1963)Studies on manganes€oxide miner- References als VII. Lithiophorite. Schweiz.Mineral. Petrogr.Mitt.,43, 197- 216. W. E. Richmond and H. T. Evans, Jt. (1962) Studiesof Agiorgitis, G. (1969)Uber differential-thermoanalytischeund in- the manganeseoxides V. Ramsdellite,MnO2, an orthorhombic frarotspektroscopischeUntersuchungen von Mangan-Mineral- dimorph of pyrolusite.Am. Mineral., 47, 47-51. ien. TschermaksMineral. Petrogr.Mitt., I j,2'13-283. Frondel, C. (1953)New manganeseoxides hydrohausmannite and Bardossy,G. and G. W. Brindley (1978)Rancieite associated with woodruffite.Am. Mineral., 38,761-7 69. a karstic bauxite deposit.Am. Mineral., 63, i63-76j. U. B. Marvin and J. Ito (1960a)New data on birnessite Brenet,J. P., J. P. Gabano and M. Seigneurin(1958). Transforma- and hollandite. Am. Mineral., 45, 871-875. tions thermiques d'oxydes de manganese.ln Papers presented _ and _ (1960b) New occurrencesof todoro_ To The Section On Inorganic Chemistry (I6th Internatianal Con- kite. Am. Mineral., 45, 1167-1173. gress Of Pure And Applied Chemistry,Paris, 1957),p. 69-80. Gattow, G. and O. Glemser(196la) Darstellungund Eigenshaften Butterworth ScientificPublications, Londoq. von Braunsteinen.II (Die y- und 4-Gruppe der Braunsteine).Z. BrowrL F. H., A. Pabst and D. L. Sawyer (1971) Bimessite on anorg. allg. Chem.,309,20-36. colemanite at Boron, California. Am. Mineral., 56, lO57-1M4. _ and _ (l96lb) Darstellung und Eigenshaftenvon Burns, R. G. and V. M. Burns (1975)Structural relationshipsbe- Braunsteinen.III (Die e, p, und a-Gruppe der Braunsteine,uber twe€n the manganese(IV)oxides. In A. Kozawa and R. J. Ramsdellite und uber Urnwandlungen der Braunsteine). Z. Brodd, Eds.,Manganese Dioxide Symposium,Vol. l, p. 306-32j. anorg. allg. Chem.,309, l2l-232. 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