BISMUTOFERRITE, CHAPMANITE, and "HYPOCHLORI'te''* Cuenrns L

THE AMERICAN MINERALOGIST, VOL 43, JULY AUGUST, 1958

BISMUTOFERRITE, CHAPMANITE, AND "HYPOCHLORI'TE''*

Cuenrns l,{rr,row, Josoru M. Axnrnoo, axo Ble.Ncne INGnalr, Lt. S. GeologicalSurvey, Washington 25, D. C. Assrnacr Bismutoferrite, Bi(OH)Fe:(SiO+)z or BizOr.2Fe:Or 4SiO: HzO in substantial agreement I'ith Frenzel's (1871) BizFerSirOrz,occurring as a yellow powder associated with bismuth ores at Schneeberg, Saxony, and nearby localities, gives a unique r-ray diffraction pattern and consistent chemical analyses. It is therefore to be considered a valid mineral species.The term "hypochlorite" has been used for a green mixture of bismutoferrite with quartz and chalcedony. The original analysis in 1832 rvas of such material; the 6rst analysis of reasonabiy pure bismutoferrite was by Frenzel in 1871. A substancealso termed "hypochlorite" was found at Briiunsdotf, Saxony, but it contains antimony instead of bismuth. Recognition of the composite character of "hypochlorite" and uncertainty as to whether it contained bismuth or antimony or both, with failure to accept Frenzel's work as valid, have until now left the status of bismutoferrite and "hypochlorite" dubious. Data pre- sented here estabiish chapmanite (Walker, 1924) as the antimony analogue of bismutoferrite. Recognition of the proper valence states of antimony and iron (both three) in chapmanite Ieads to a correct interpretation of the formula from the original analysis. Bismutoferrite and chapmanite therefore form a homologous and presumably isostructural group of two valid species; the name "hypochlorite," which has been used to designate a characteristic mixture of either of these minerals dispersed in quartz or chalcedony, may well be discarded.

Hrsronrc,q.r "Hypochlorite" was the name given bySchiiler(1832) to a highly silice- ous bismuth-bearing yellow-greenmaterial from Schneeberg,Saxony. Dana (1870) summarizedthe original account as follows: "minute crys- talline, also earthy: H:6, G-2.9-3.04.Color green, streak light green, brittle, fracture even to flat conchoidal,"and he citesan analysis(Table 3, A). Schiileris quoted by Frenzel(1871) as saying that "hypochlorite" occurs rarely; associatedwith quartz, chalcedony,bismuth, cobaltite, and arsenopyritein veins in shaleat Schneeberg:with quartz, bismuth, galena,and silver ores in mica schist at Johanngeorgenstadt;and with q\artz and pyrite in mica schistat Briiunsdorfnear Freiberg. Frenzel states that Schiiler'sanalysis was forthwith consideredto be of a mixture, the questionbeing raisedby the editor of the journal that published Schiiler's paper; and this view was concurred in by Dana (1868),Breithaupt (1871),and H. Fischer(1870), who pronouncedit to be microscopicallya mixture of three substances,namely, q\artz, an opaque green substanceas the most abundant constituent, and radial

x Publication authorized by the Director, U. S. Geological Survey. 6s6 BISMUTOFERRITE,CHAPMANITE, AND "HYPOCHLORITE, 657 spheroidalaggregates of brown need.les.(The "opaque greensubstance" ,,hypochlorite,' presumablywas the proper, and the brown needlespos- sibly goethite.) A few years after Schiiler's report on (bismuth) "hypochlorite," a paper by Kersten (1844)appeared, giving an analysisof the "hypochlo- ritl" from Brdunsdorf("Neu Hoffnung Gottes") in which he found antimony, but no bismuth. This apparent conflict with the earlierwork may well have contributed to the misgivingswhich becameassociated with thesesubstances.

The following ye^r, in 1872,Frenzel further discussed"hypochlorite,"

preciseobservations, but which were apparently monoclinic' We may observehere that our own work, almost a century later and with modern tools avaiiable, fully confirms that of Frenzel, and we

also been found in Alaska by W. T. Schaller,U. S' GeologicalSurvey (personalcommunication). Chapmanite with quattz (antimony-"hypochlorite") also occurswith sulfideore from Velardefla,Durango, Nlexico. Nevertheless,Frenzel's contemporaries and successorswere not con- vinced of the validity of his work, and bismutoferriteand "hypochlorite" have beenconsigned to the limbo of discreditedspecies or mixtures.Thus Dana (1892)refers to Schiiler's"hypochlorite" as "beyond doubt a mixture," and to Frenzel'sbismutoferrite as a "supposedbismuth iron silicate." Doelter (1917)notes that bismutoferriteis a mixture, like "hyPo- chlorite." Ramdohr (1936)lists bismutoferriteas an obsoleteterm for a mixture of bismuth and iron minerals, and "hypochlorite" similarly. Hey (1950)refers to "hypochlorite" as "very doubtful; probably a mixture," and lists bismutoferritein small type, that is, not of speciesrank' 658 c. MILTON, J. M. AXELROD,AND B. INGRAM

,,olive-green" In 1924, Walker described an powdery mineral from south Lorraine, ontario, whose compositionwas given as 5Feo.Sbzor '5SiO2 2HzO and which he named chapmanite. Except for ferrous instead of ferric iron and other minor variations, this formula is not greatly different from that of bismutoferrite, 2FezOsBrrOa.4SiOz HrO. From the extremely closesimilarity of the r-ray difiraction patterns (Table 6), the calculations of average index of refraction by Gradstoneand Dale's Iaw as given below, and critical review of the originar walker-Todd analysis of chapmanite, it will be shown that bismutoferrite is homologous (isostructural?)with chapmanite. Although chapmanite has been ac- ceptedas a recognizedspecies, its relationshipshave not beenknown, nor has it been reported until now from any locality except the original ontario source.walker's formula, as will be shown, is erroneous,and be- causeof this the relationship between bismutoferrite and chapmanite has gone unrecognized.

Merpnrar Sruprpo aNn AcTNowLEDGMENTS At the suggestionof Clifiord Frondel, of Harvard University, we have restudiedall availablematerial labeled bismutoferrite,chapmanite, and "hypochlorite," (as well as stibiaferrite,l (Goldsmith, 1g73) and ju_ juyite,2 (Ahlfeld, 1948)both of which have beenfound to be unrelatedto this presentstudy). To him and to GeorgeSwitzer, of the united states National Museum, and Brian Mason, of the American Museum of Natural History, New York City, all of whom supplied the specimens studied,we expressthanks. Michael J. Milton studied the specimensby the r.-ray fluorescencemethod (Adler and Axelrod, 1956) in the U. S. Geological Survey. Robert G. coleman and Alfred H. Truesdeil, also of the GeologicalSurvey helped greatly in the purification of the analyzed sample of bismutoferrite, in particular by removal of microscopic parti- cles of sulfidesthrough the use of the Mayeda flotation ceil (Kerr, 1950). The 30 specimenslabeled "hypochlorite" or bismutoferrite from the three Museum collections that were examined fall into four groups. as follows:

Group r contains more or less pure bismutoferrite, all from saxony. Group rr contains bismutoferrite dispersed in quartz or chalcedony, that is, "bismuth hypochlorite"-all from Saxony. Group IfI contains chapmanite dispersedin quartz or chalcedony:

I stibiaferrite has been studied by vitaliano and Mason (1952) and found to consist of wulfenite, bindheirnite, and jarosite in quartz. 2 Jujuyite also studied by Brian Mason (personal communication 195i) is tripuhvite and quartz. BISMUTOFERRITE,CHAPMANITE, AND "HYPOCHLORITE" 659

that is, antimony "hypochlorite"-all from Saxonyexcept one from ntlexico and one from Hungary. Group IV is a miscellaneouslot of mislabeled specimensmostly nontronite, only one of which is reportedas from Saxony.

Others specimensfrom the National Museum labeledchapmanite included three more or lesspure chapmanitesfrom Ontario; and one from Aiaska, termed "hydrous ferrous antimonate" (W. T. Schaller) which hasbeen identified as essentiallyantimony "hypochlorite" or chapmanite dispersedin silica. Two others labeled chapmanite from Ontario from the American Nluseum of Natural History collectionsare also chapmanite from the type Ontario locality.

Group L Bismwtoferrite Table 1 lists specimensidentifi.ed as bismutoferrite. All of these are either soft, bright yellow and powdery, or hard and green;all tested (by r-ray fluorescence)are essentiallycompounds of bismuth and iron (and silica, not detectableby the r-ray spectrographicmethods used), and have at most traces of antimony; eight are from Schneeberg,and one from Ullersreuth;noneis from Brdunsdorf. A consistentr-ray diffraction pattern (Table 6) was obtainedfrom the six of theseso examined.Chemi- cal analysis(Table 3, C) gave a reasonableformula, Bi(OH)Fez(SiO+)2, in striking agreementwith the older analyses(Table 3, D and E) on which Frenzel basedthe speciesbismutoferrite.

Group IL Bis muth-" hyp ochlorite" (Quartz and,bis mutof errite) In Table 1, Bismutoferrite, it will be noted that Harvard 47001 is representedby three r-ray diffraction patterns, two of "hard green" material, one of "soft yellow," the former identified as quartz and more or lessbismutoferrite. By r-ray fluorescenceall three spindlesshow major bismuth and iron, and no antimony. In this specimenboth types of material are presentin sharply definedareas. Materiai of the same na- ture, but more easily recognizedas essentiallydrusy quartz, is present in the five specimenslisted in Table 2. Chemical analyses substantiating the *-ray fluorescenceare given in Table 3: Schiiler'soriginal analysisof "hypochlorite" (A and B) and Frenzel's (F).

Group III. A nt'imonlJ' hyf ochlorite" (Quartz and chapmanite) So far, all the substancesdescribed have beenbismuth minerals,essentially pure or admixed, with no antimony. We now come to a group of eight specimenslisted in Table 4, Group III, very much alike, all char- 660 C. MILTON, J. M. AXELROD, AND B. INGRAM

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A C D E F G

Biros 13 02 13.08 42.5 43.26 42.83 4.76 M.65 Al2o3 14 65 14.65 .3 sio, 50.24 50.34 239 23 08 zlrls I **t 23.02 FeO 1.8 Fe:O: 10 54 10.54 29.3 33.33 30.60 sbzo: PzOs 9.62 9.62 As:Oa .08 HuO+ 1.6 1.73 SO:MgOMnO trace

98 07 98 23 99.7 100.00 sp.gt. >33

A. "Hypochlorite,"Schneeberg,G.schiiler,analyst(Schiiler,1832),ascitedinDana,3rd Ed. (Dana,1870). B. "Hypochiorite," Schneeberg,G. Schiiler, anaiyst (Schtiler,lg32), as cited by Frenzel (Frenzel,1871). C. Bismutoferrite, Schneeberg,Blanche fngram, U. S. Geol. Survey, analyst, 1956, Har- vard 46981. D. Bismutoferrite, Schneeberg,A. Frenzel, analyst (Frenzel, 1871). E. Bismutoferrite, Schneeberg,A. Frenzel. analyst (Frenzel,18Z2). F. Bismuth-"hypochlorite" (quartz and bismutoferrite), A. Frenzel, analyst (Frenzel, 1871). G. Bismutoferrite, theoretical, Bi(OH)Fez(SiOr)2.

acterizedby antimony and containing no bismuth. They contain a min- erai dispersedin quartz or chalcedony, with an n-ray difiraction pattern almost identical with that of bismutoferrite.This mineral is chapmanite. discussedbelow. rt will be observedthat Harvard 46972is labeledas from Schneeberg; three other Harvard specimens,apparently very similar to it, are as- cribed to Briiunsdorf. Schneebergis the probable sourceof all the bismuth minerals in question,and Brdunsdorf, of the antimony minerals. The original label of this particular specimenhas beenlost (c. Frondel, personalcommunication, 1956) and the presentlabel may well be erroneous. our questioningof the Schneeberglocality for Harvard,46972 and suggestionthat it too should be Brd.unsdorf,is borne out by Frenzel's statement (1871,page 361) that no bismuth minerals occur at Brduns- dorf. The first four specimensare similar in appearance; hard, dull olive- green, massive, with small holes; they form part of qtrartz veins, with pyrite and associatedminerals, between the green mineral and the vein BI SM UTOF ERRIT E, CHA PM A N IT E, A N D " H YPOCH LORI TE"

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Tesrn 5. An.^r,vsnsor "ANrruoNv-Hvpocnr,omrn" (euln:rz lwo cne'u,rNrrr) AND LHAPMANITE

Sbzo: 3.01 50 s56 /.J 336 SbzOs Jl.o.) SiOz 88.50 86.0 86.40 78.0 28 28 276 FeO 33.91 Fezos 5.01 7.8 8.04 ll.+ 36.8 P:Oa 2.03 trace trace HzO 100 1.0 346 2l Nio .36 CoO .03 Cu .ll Bi .20 As 1.28 Al2o3 .28

99 55 98.8 99.62

H. "Antimony-hypochlorite,', Brriunsdorf, Kersten, analyst (1g44) (SO3, MgO, MnO, trace). I. "Antimony-hypochlorite,', Briiunsdorf , A. Frenzel, analyst (1g71). J. "Antimony-hypochlorite,,, Brdunsdorf, A. Frenzel, analyst (1g71). K. "Antimony-hypochlorite," Briiunsdorf, A. Frenzel, analyst (1g71). L. Chapmanite, Ontario, E. W. Todd, analyst (Walker 1924). M. Chapmanite, theoretical, Sb(OH)Fez(SiO):. qnartz- Microscopically, the color is seen best with the condenser in, under high magnification.The needlesare too small for optical studv: their abundanceagrees with what would be expectedif Kersten'sanalysis (Table 5, H) is of a mixture with quartz. The fifth specimenin Table 4 is mostly nontronite, containinga rittre antimony "hypochlorite.,, A somewhat nondescript material (u.s.N.M. 10s222)coilected by B. J. l\llertie, of the U. S. GeologicalSurvey, in 193g, from Venesela Mountain, Alaska (Lat. 60"47' N Long. 155o43'w) containing iron, antimony, and water, was found by x-tay to be essentially the ,i,'" u, the Brd.unsdorf"antimony hypochrorite," that is, chapmanite,dispersed Ln quartz. Analyses of the material-.(antimony hypochlorite,,' actually, chap_ manite dispersedin quartz or chalcedony-are given in Table 5. Also, in this table, are given the originar analysis of itre ontario chapmanite (walker, ]924); and the true composition inferred from its relationshio to bismutoferrite. rt will be observed that the two analyse. u." '* greatly different. x-ray data are given in Table 6 for bismuioferrite and chapmanite. 665 BISMUTOFERRITE, CHAPMANITE, AND''HYPOCHLORI.TE"

Gr-ensroNn',lrql Detn's L.q.wAppr-rBp ro BrsuuroFERRrrE ,qNt CHepxlaxrrl,

of the untenability of Walker's formula for chapmanite'

Available data are: For bismutoferrite (a) indicesof refractionq:!'93, P:l'97, t:2'o1 (determinedby us) (b) density 4.47 (Frenzel,1877) (c) propcsed formula BizO:'2FezOr'4SiO, HrO Berman (1934) (j; .p"iin" refractive energiesof above oxides, as given by Larsen and except for Fe2Or' as given by Jatre (1956).

For chapmanite (a) indices of refraction a:1.85, t:1.96 (Walker, 1924) (b) density 3.58 (Walker, 1924) (c) proposed formula Sbror 2Fe:O;'4SiOz'HzO Waiker's formula SbzOo'5FeO' SSiOz'2HrO for Sb:or 0.209 (d) Specific fefractive energies of above oxides with alternate values and'0.232 and for SbzOs0.152 and 0'222 (Larser' and Berman' 1934)'

Calculation using this data gives Indices of I{efraction Average Average Density Observed Observed Calculated

Bismuto- ferrite 4 47 a:I.93 tt:I.97 t:2'01 r.97 t.96

Chapmanite (Correct q6 1.89 formula) 3.58 a: 1.85 -:1 1.905 1.86,

Chapmanite (Walker's formula) 3.58 e: 1. 85 t:I .96 1.905 1.673,1.752 Evidently, the agreement of observedaverage index of refraction with (our the calculatedindex for bismutoferriteis excellent;for chapmanite poor' formula) good; but for chapmanite, using Walker's formula, very Tn sum-a.y, application of Gladstone and Dale's law supports the 666 C. MILTON, T. 1,[. AXELROD,AND B INGRAM

formula Bizor'2Fezos 4sio2 Hzo for bismutoferrite,and sbzoa.2Fezoe '4SiOz HzO for chapmanite.

Tun CouposrrroN on Cuaplraxrrp still other reasonsexist for rejecting E. w. Todd,s (walker, 1924) analysis of chapmanite and walker's formula based upon it. Michael Fleischerhas pointed out (oral communication) that the formula derived from Todd's analysisis open to seriousquestion. walker says that ,,the state of oxidation of the iron was determined by dissolving the mineral in hydrofluoric acid and titrating with potassicpermanganate.', Todd and walker assumedthat lerrous iron was thereby oxidized to ferric. rn our opinion, what actually happenedwas that antimonousoxide was oxidized to antimonic. rndeed, titration of antimonous salts with permanganateis a standard analytical method for the determination of antimony (scott, 1939).considering the two oxidation reactions, 2SbrOsf4O:2SbzO; 2FeO f O:FezOr it is evident that the amount of oxygen (or the equivalent permanganate) necessaryto oxidize four moles of Feo is equal to that necessaryto oxidize one mole of SbrOs.Todd, therefore,mistook the oxidization of a mole of Sbzosfor the oxidation of a substantiaily equivalent amount (actually, five moles)of Feo. He was,of course,familiar with this stand-

walker further notes that "at 270othe mineral rost its greencolor and becamepale brownish,due, apparently,to a changein the state of oxidation which would result in an increaseof weight." we do not regard this color change as necessarilyindicating oxidation of ferrous iron; it could reflect decomposition of the silicate mineral, with releaseof ferric oxide as such. I'Iany ferric silicates are green, not yellow or brown. Unlike SbzOr,BizOg is not oxidizedby permanganate.Titration of FeO in bismutoferrite by permanganate as in r{rs. rngram,s analysis is thereforea valid procedure;and it may be noted that shefound the iron presentto be almost wholly ferric iron. Finally, the remarkable similarity oI the x-ray difrraction patterns of bismutoferrite and chapmanite is further weighty evidence for their formulas being homologous.we therefore reject walker,s formula for chapmanite and accept chapmanite as Sb(OH)Fez(Sioa)ror SbzOa '2Fezot 4Sioz Hzo, homologous or isostructural with bismutoferrite Bi(oH)Fez(Sion),or Bizoe.2Fezo3.4sio2. H2O. BISMUTOFERRITE, CHAPMANITE, AND "HYPOCHLORITE" 667

,,hypochlorite Frc. 1. Thin section of (bismutoferrite in quartz), Schneeberg, Saxony. Harvard 274. Shows typical aspect of "hypochlorite" (the same for both bismuth and antimony types). At the edgesof the dense aggregatesof bismutoferrite,extremeiysmall, poorly developed single crystals are discernible. Ordinary light.

X-n.tv Darn Except for the several specimenswhich were identified as nontronite and other extraheous species,#-ray powder patterns of the specimens Iabeled"bismutoferrite" and "hypochlorite", and chapmanite included one distinctive pattern. The pattern varied slightly from sample to sample, as is not unusual for a mineral species.However, when r-ray spectroscopyshowed a mutual exclusion of bismuth and antimony, the most obvious variation, that in the relative d-spacingsof a medium intensity triplet around 2|5gh,was re-examined;the triplet 2.66-2.59-2'fih is characteristicfor the bismuth mineral and the triplet 2.67-2.59-2.54h is characteristic for the antimony mineral. Other variations in spacing conform so there are actually two slightly different patterns, those of bismutoferrite and chapmanite. Intensity relationship differences between the two patterns in Table 6 result at least in large part from preferred orientation in bismutoferrite. Lines obviously strengthened in some patterns by preferred orientation are marked by a plus sign and those weakenedare marked by a minus sign. C. MILTON, I. M. AXELROD, AND B. INGRAM

Tanr,n 6. X-Rly Powoon DrrlnacrroN PamrnNs ol, Brsu.ulrolnnnrro eNo CnapuaNrm \r I )' ).:1.s4Vh(culNi) i .' r:114.6 mm.

Bismutof errite Chapmanite Bismutoferrite Chapmanite HMM 46981 u.s.NM. 94866 HMM 46981 u s N.M. 94866 Film No. 8912 FilmNo. 11748 Film No 8912 FilmNo. 11748 Max. d-spacing Max. d-spacing Max. d-spacing Max. d-spacing cutoff 14 73 cutofi 13.59 cutofi 14 73 cutoff 13.59

d I d I d d ,/ . o.t 100- /.oJ 100- 1.471 3 1.471 4.52 6- 1.456 L 447 6 4.44 3 1.451 1 418 18+ 4.17 25 r .4J.) 4 .443 5 3.87 100- 3.88 90- |.394 1b .397 5 3.79 2 3.80 5 1.370 i .373 12 3.58 35'+ 3.58 100 1.360 1 3.18. s0+ 3.19 90 r.329 1 2.90 70' 2.90 70 1.299\ 1 .296 9 2.66 12+ 2.67 ZJ | .2e11 1 2.59 259 70 1.282 <1 .281 3 z-J,) 25- )\L J.) t.257-1.252 1 2.383 l0 2.380 18 .24t 2 2.3M 9 1.224 1 228 3 2.287 3 1.215 I .221 5 2.25r 9 L Z+J 18 1.203 2 .204 5 2.225 3 1.184 1 2.201 9- 2.217 18 1.176 <1 2.162 15- 2.156 18 1.169 1 1.167 2 .086 5 2 .085 18 1.161 <1 2 040 9 2.044 18 1.143 1 l.t+2 2 2.Or1 1 , 7.124 1 |.124 o 1.976 <1 1.106 <1 1.109 3 1.935 12- 1 911 l.) 1.093 1 r.907 o 1.910 18 1.080 1b 1.891 6- 1.067 <1 1.863 3 1.873 5 1.049 I 1.835 3 1.838 6 r.037 <1 .016 2 1.785 1 r.,/d.) 9 .9830 2 .9826 5 1.744 3 9736 <1 1.719 l2 1.725 22 9418

b:broad line. f :band with peaks. *:strengthened by preferred orientation. - :weakened by preierred orientation. 669 BISMUTOFERRITE, CHAPMANITE, AND "HYPOCHLORITE,

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The patterns of the two minerars are remarkably similar and the pair may be classedwith such pairs as scheerite-powelriteand magnesite- siderite in which one element completely substitutesfor another with very little change in the *-ray patterns.

,,Hypochlorite,, Group IY, Miscellaneoussubslances lermed, or ,,Bismuto_ ferrite" rn all three Museum collections were found specimenslabeled ,,hypochlorite" which proved to be something different. These are listed in Table 7. Apparently nontronite is easily mistaken for ,,hypochlorite,, which it superficially resembles.

Btlr,roGn,tpttv Alrnn, I., alo Axrr,non, J" M., 1956, Application of X_ray fluorescence spectroscopy to analytical problems: Norelco Reporter, v. 3, 65_6g.

Frscrrn, H., 1870, critische, mikroscopisch-mineralogische Studien: Berichte der Naturf . Gesellsch.,Freiburg, Band 5, Hft. 2, pp. 1-64. Fruwznr, A., 1871, Hypochlorit: Journal prakt. Chemi,e,(N.F. 4) 353_362. FnrNzrr,, A 1872, Letter to prof. ' H. G. Beinitz: Neues rohrb fiir Minerar.,514-517. Gor.osurrn, 8., 1873, Proc. Aco.d..philadetOhia. 366. Hnv, M. H., 1950, Chemical fndex of Minerals, pp. 102,lgg.British Museum, London. H. w., 1956, Jerrn, Application of the rule of Gladstone and Dale to minerals, Am. Mineral., 41, 757-777.

RenooHn, P., 1936, Klockmann's Lehrbuch der Mineralogie, Enke Verlag, Stuttgart, pp. 601, 603. ScHiir'rn, 1832, sogenannter Griineisenerde von schneeberg, Hypochlorit: Jour. Jiir Chemieund. Phys,ih,66, p. 41. Scom, W. W., 1939, Standard methods o{ chemical analysis, p.76,D. Van Nostrand & Co., New York. vrter.raNo, c. J., aono Masor.r, Bnralr, 1952, stibiconite and cervantite : Am. M.inerol., 37,982499. Wer.rrn, T.L., 1924, Chapmanite, a new mineral from South Lorraine, Ontario, (Jnir. oJ Toronto Stud.ies,Geol. Ser.17, p. 5.

Manuscri.pt rece.iaedOctober j0, 1957