THE AMERICAN MINERALOGIST, VOL. 47, JANUARY-FEBRUARY, 1962

STUDIES OF THE MANGANESE OXIDES. V. RAMSDEL-LITE, MnO2, AN ORTHORHOMBIC DIMORPH OF

PYROLUSITEl

Mrcnapl FlBrscnpn.2 W. E. RrcuMoND.s ANDHowano T . EvnNs, Jn .2

ABSTRACT

Ramsdellite is an orthorhombic dimorph of pyrolusite; the composition is close toMnoz with no certain deviation from that composition. rt inverts to pyrolusite at about300'; the inversion is presumed to be monotropic. Examination of crystals from theGavilan Mine, Mexico, shows them to be pseudomorphs after groutite; a secondary latticeis probably that of an intermediate stage of oxidation. chemical analyses and *-ray dataare given, and the physical properties are summarized.

fNrnooucrroN

Early in 1941, in the course of an extensive study of manganese oxideminerals, a sample collected by S. C. Creasey of the U. S. GeologicalSurvey from Lake Valley, New Mexico, was found to give a distinctivefi.-ray pattern. Analysis showed that the composition was close to MnO2;at our request Mr. Creasey collected a large suite of samples. Through thecourtesy of Professor L. S. Ramsdell of the University of Michigan, weobtained his specimen, from an unknown locality, of a dimorphous formof MnOz (Ramsdell, 1932); it proved to be the same mineral as that fromLake Valley. It was named ramsdellite and a preliminary report, in whichthis name was used, was published in 1943 (Fleischer and Richmond,1943). At that t ime, chemical analyses had been made, the inversion topyrolusite had been noted, and a preliminary determination of the unitcell had been completed.

Shortly thereafter, Dr. Richmond left the U. S. Geological Survey, andFleischer was assigned to more urgent work for the Manhattan Project;various circumstances have unfortunately prevented the publication ofthe data on which the new mineral name was based. We have, however,supplied many investigators the world over with samples from LakeValley, and some twenty papers dealing with the mineral have appeared;all the data on Lake Valley samples cited were obtained on samples sup-plied by the U. S. Geological Survey. This paper gives our data and sum-marizes the published information.

Cunurstny

All available chemical analyses of ramsdellite are assembled in Table 1.The composition is close to MnO2, but the ratio of total cations to oxygen

1 Publication authorized by the Director, U. S. Geological Survey.2 U.S. Geological Survey, Washington, D. C.3 R.F.D. No. 2, Hillsboro, N. H.

47

48 M. FLEISCHER,W. E. RICHMOND AND H. T. EVANS, JR.

Talle 1, Cnnurc,lr, Axer-vsns ol Reusoelltrr

MnOzMnOMsoZnOBaOCaONarOKzOH:O-

H:O+AhOrFezOeSiOzTiOzPsOu

0 . 2

IJ 1 . sl.0 . 81 . 20 . 80 . 2

0 . 9 60 . 1 6

(\ o . o zI

97 .14"none0 1 2

n.d.bnonenone

0 . 3 10 . 4 1(I

1r . z+II0 .480 . 3 40.42

nonenone

95.O2"nonenone

0 . 250nonel . r 2

present, n.d.present, n.d.

0.05

r . 3 90 . 7 20 . 2 20 . 3 6

nonen.d.

0 . 6 8 0 . 2 8tt' tt-

(I

i 0 . 9 6t

Y t'r

100 46

Active O' 17 .88Total Mn 61 .00Active O/Mn 1.006G . 4 . 7 3

99. r3

17 .4959.621 .0074 . 6 5

61.28 60 .17

4 . 8 3

* calculated from active o; determination by the method of Fleischer (1943). Active

O:oxygen reactive with oxalic acid, that is, oxygen above the requirements for MnO'b Shown by K. J. Murata spectrographically to contain about as much Zn as No. 2.

" Determined by C. M. Warshaw on a separate portion of the same sample'

1. From Lake Valley, New Mexico, analysis by Michael Fleischer in 1942; X-ray study

showed that the sample contained considerable pyrolusite.

2. Locality unknown, Ramsdell's type specimen; analysis by Michael Fleischer in

1942; X-ray study showed a very small amount of pyrolusite'

3. From Lake Valley, Bystrdm (1949).

4-6. Three difierent samples from Lake Valley, analyses by Charlotte M. Warshaw in

1951; X-ray study showed very small amounts of pyrolusite.

is not known because of the uncertainty as to the role of zinc (present in

all the Lake Valley samples), calcium' alkalies, and H2O. The SiOz,

Fe2O3, and, AIzOs present are assumed to be due to impurities (chert and

iron oxide are known to have been present). Spectrographic analyses by

K. J. Murata showed that beryll ium, cobalt, nickel, thall ium, and

vanadium were absent in samples I and 2 of Table 1 and showed traces of

lead and 0.0X per centZn in ramsdell ite from the Gavilan Mine, Lower

California, Mexico. A semiquantitative spectrographic analysis was

RAMSDELLITE, ORTHORHOMBIC DIMORPH OF PYROLUSITE 49

made by Nancy M. Conklin in 1959 of another sample from Lake Valley;she found (weight per cent) Mg 3, Ca 0.15, Fe 0.C15, Zn 0.7, Ag 0.015,Cu 0.003, Mo 0.03, V 0.015, W 0.003, Pb 0.3, Ba 0.07, S 0.007, andY 0.003.

As discussed later in this paper, ramsdellite is related structurally togamma-MnO2 (or Nsuta MnO2, Sorem and Cameron, 1960), which isgenerally believed to be a defect structure with Mn:O less than 2.Wadsley and Walkley (1951) state, "A specimen (of ramsdell ite fromLake Valley) has been analyzed by the authors, and in common with allthe manganese dioxides shows a departure from true stoichiometric pro-portions. The cell dimensions and the thermodynamic properties shouldtherefore be capable of some variation." The analysis unfortunately islost (A. D. Wadsley, priv. comm. to Fleischer, 1960). The published *-raydata on ramsdell ite (Table 3) show no indication of compositional varia-tion.

Bpuevron WuBN Hnaroo

Ramsdell (1932) reported, "After heating to a low dull red heat, a nor-mal pyrolusite pattern was secured. This heating was accompanied by aIoss of water of only 1 per cent and the total loss in weight was less than 2per cent. This would seem to eliminate either dehydration or a changefrom some other oxide as a cause of the change in pattern. A possible ex-planation is that this specimen represents an unstable form of MnO2,which is converted to the normal form by heating."

We confirmed Ramsdell's observations in studies of Lake Valley ma-terial. Samples heated in air at 200or for 4 days and at 240" for 7 daysshowed no change in *-ray pattern, but a sample heated at 310o for 5 dayshad been converted almost entirely to pyrolusite (r-ray data by J. M.Axelrod). Klingsberg and Roy (1959) found that ramsdell ite from Chis-holm, Minnesota, was unchanged when heated in air at 316o for 4 days,but gave a trace of pyrolusite when heated at 313" for 14 days. They alsoreported that groutite, MnO(OH), changed slowly to ramsdell ite above130", changed in a few hours at 300", but above 300o it went directly topyrolusite.

Difierential thermal analysis curves for ramsdellite have been pub-Iished by McMurdie and Golovato (19a8) (Lake Valley), Kulp and Per-fetti (1950) (Idorado Mine, Colorado), and by Cail lbre and Kraut (1954)(locality not stated). Kulp and Perfetti found a small endothermic peakat l2Do (capillary water) and an exothermic break at 500o correspondingto the inversion to pyrolusite. Cailldre and Kraut found a break at 450o.McMurdie and Golovato report that "below the first break at 670o heat

t This and all other temperatures are "C.

50 M. FLEISCHER, W. E. RICHMOND AND H. T, EVANS, JR.

was being absorbed and r-rays indicated a change to pyrolusite. This

change from ramsdellite to pyrolusite does not appear to occur sharply or

to be accompanied by a large energy effect, and is not reversible." After

the inversion to pyrolusite, the D.T.A. curves, as might be expected, are

essentially identical with those given by pyrolusite, except that Caillbreand Kraut report an extra endothermal break at 850o.

The inversion of ramsdellite to pyrolusite is presumably irreversible

and monotropic, although there is no direct evidence of this;very l ikely

the inversion would occur at temperatures below 300' if sufficient timewere allowed. It should be noted that neither ramsdell ite nor groutite has

ever been synthesized (Moore, Ell is, and Selwood, 1950) although they

are readily converted into one another hydrothermally (Klingsberg and

Roy, 1959).

Cnvsrar,r,ocRAPurc AND X-RAY Sruorns

The first work on the crystal structure of ramsdellite was by Rich-mond (quoted by Fleischer, t944), who determined the orthorhombic

symmetry and the approximate cell constants on cleavage fragments from

Lake Valley, and who recognized the similarity to diaspore. The struc-

ture was worked out by Bystr<im (1949) on Lake Valley material. Shefound it to be orthorhombic, space group D27,16, with the cell constantsgiven in Table 2, Z:4, sp.gr. calculated 4.84, determined 4.83' Cellconstants given by Kedesdy et al. (1957) (locality not stated), Klingsbergand Roy (1959) (Chisholm, Minn.), and Evans (this paper) (Lower

California) agree closely with Bystrtim's. The only discordant values are

those on a sample from Giiziirem, Ere{li region, Turkey, published in anabstract by Schrcider (1952), who stated that he obtained them frompowder data that agreed closely with those published by Fleischer and

Richmond (1943). Schrcider's unit-cell constants, given in Table 2, showno apparent relation to those of other investigators and give a calculateddensity ol 4.346, in good agreement with his own determined value'

4.370. More detailed data have not been published. We are unable to ex-

plain these results.Crystals of ramsdellite have not previously been described, although

X-lingsberg and Roy (1957) mention crystals as much as 6 mm long from

Chisholm, Minnesota. What appeared to be single crystals of ramsdellite

were found on samples from the Gavilan Mine, Lower California, Mexico,

kindly given to us by James A. Noble. The samples consist of massive

plumboan hollandite, with the surface incrusted by crystals of ramsdell ite

and with apparently excellent single crystals, a few tenths to two mm in

size, in fissures and cavities. When examined by Evans in 1958, these

crystals proved to be pseudomorphs of ramsdellite after groutite. Fig. 1,

RAMSDELLITE, ORTHORHOMBIC DIMOKPH OF PYROLUSITE 51

Tlsr,B 2. Cnr,r, Coxsrmtrs (rN A) or Rlusonr.r-rrr nNo Rrr,atao PHASEs

Material Reference

Ramsdellite 4.5

Ramsdellite 4.533

Ramsdellite 6.374Ramsdellite 4.528

Ramsdellite 4.52

Ramsdellite (strong phase) 4.53

Ramsdellite (weak phase) 4.61

Groutellite 4 .7I

Groutite 4.58

Grout i te 4.56

Groutite 4.56

Gamma-MnO: 4.46

Gamma-MnOz 4.418

Gamma-MnO: 4.450

Gamma-MnOz 4.470

Gamma-MnOz 4.489

Gamma-Mnor eu(OH)o 04 4.42

Gamma-MnOr sr(OH)o os 4.43

Gamma-MnOr.zn(OH)o.ze 4.49

Gamma-MnOr *(OH)o 36 4.51

Gamma-MnOr.*(OH)os 4.54Rho-MnOz 4.453

9 . 2 2 . 8 3

9 . 2 7 2 . 8 6 6t0.126 4.0929 .285 2.8669 . 2 7 2 . 8 79 . 2 8 2 . 8 69 . 5 4 2 . 8 89 . 5 2

10.76 2 .8910. 70 2 .8510.00 3 .039 32 2 .850

9 51 2 .8 t19 305 2 .8509.336 2 .8489.391 2 .8489 . 7 0 2 . 7 9 09 . 7 0 2 . 7 9 t9 .79 2 .8209.93 2 .8+o

1 0 . 2 0 2 . 8 5 e9.396 2 .827

Richmond (in Fleischer,

reM)Bystrdm (1949)Schrdder (1952)Kedesdy et al. (1957)Klingsberg and Roy (1959)Evans, this paperEvans, this paperKlingsberg and Roy (1959)Collin and Lipscomb (1949)Gruner (1947)Klingsberg and Roy (1959)Kondrashev and Zaslavskii

(1es1)Kedesdy et al. (1957)

de Wolfi (1959)

de Woltr (1959)

de WoIfi (1959)

Feitknecht et al. (19ffi)

Feitknecht et d. (1960)

Feitknecht et a). (1960)

Feitknecht et, al,. (196O)

Feitknecht et al. (196O)

Kedesdy et al'. (1957)

2, (from Lake Valley), and 3 show three typical forms. The wheel-shaped

crystal (Fig. 3) is very similar to a crystal of groutite figured by Gruner(1941). Professor Paul Ramdohr has kindly called our attention to the

similarity of Fig. 1 to a drawing of a crystal figured as "pyrolusite" in

Dana's System of Mineralogy, 5th Ed., 1868, p. 165.The faces gave poor signals on the goniometer and were not measured

accurately; ,tulll}l was prominently developed on most crystals and

o the r f aces i den t i f i ed we re D{010 } , o [100 ] , c {OOt } , / { 011 } ' y l l 2 } l ,

f r {130 } , e l \ 2 r l , Q l24 r l .Buerger precession patterns gave a unit cell identical with that of

Bystrdm (1949), but a second, less prominent lattice was also present'

similar to that of ramsdellite, but with a slightly larger unit cell. The

measured lat t ice constants are ( in A) :

Strong phase (Gavilan Mine)Lake Valley (Bystrdm, 1949)

Weak phase (Gavilan Mine)

4 .53 +0 .02 9 .28+0 .03 2 .86 +0 .024 .533+0 .005 9 .27X0 .01 2 .866+0 .0054 .61 +0 .04 9 .54+0 .05 2 .88 +0 .03

52 M. FLEISCHER, W. E. RICIIMOND AND II. T. EVANS, JR,

Frc. 1. (Left) Ramsdellite after groutite, Gavilan Mine, Lower California, Mexico. t {010},m lll0l, y ll20l, J [011]. Drawing by Evans.

Frc. 2. (Right) nu-.d"rft ", ffi -d.[lt,. tjl;I?';i

il",:J*tco. b [ 010 ]' nt' {rt't,

The patterns were somewhat diffuse for both the strong and weak phases.Traces of a pattern due to a pyrolusite lattice in parallel orientation werealso present on the photographs; this lattice is oriented so that the tetrag-onal a, b:a, and c axes of pyrolusite are parallel to the orthorhombica, b, and c axes, respectively, of ramsdellite.

The ramsdellite crystals are therefore pseudomorphs after groutite,Iike those found by Klingsberg and Roy from Chisholm, Minnesota, andare formed by the oxidation reaction aMnO(OH)*Or--+4MnOz+2H2O.Exactly the same reaction is involved in the conversion of manganite topyrolusite. Pseudomorphs of pyrolusite after manganite (MnO(OH)) arewell known. Another example, found at Lake Valley, New Mexico, isshown in Fig. 4. The *-ray pattern of the pyrolusite crystal shown exhibitsthe same kind of difiuseness as that of the ramsdellite pseudomorphsfrom Gavilan Mine. These conversions are readily understood on thebasis of the crystal structures of the phases involved. The structure oframsdellite is essentially similar to that of groutite, so that the latter cantransform to the former by a diffusion of the hydrogen atoms to the sur-face of the structure, where they react with atmospheric oxygen, whileonly minor adjustments are required for the positions of the manganeseand oxygen atoms. A similar controlling structural relationship exists be-tween manganite and pyrolusite. Such an alteration process may be ex-pected to disturb the periodicity within the large crystals sufficiently toaccount for the difiuseness of the r-ray photographs of the altered phases.

RAMSDELLITE, ORTHORHOMBIC DIMORPII OF PYROLUSITE 53

Ftc' 3. (Left) Ramsdellite after groutite, Gavilan Mine, Lower california, Mdxico. c [001],, {010}, a [100] , m l l l0 l , e {130}. Drawing by Evans.

Frc. 4. (Right) Pyrolusite pseudomorph after manganite, Lake Valley,New Mexico. Drawing by Evans.

The hypothesis of alteration also parallels that proposed for the pairmontroseite [Vo(OH)]-paramontroseite (VOz) by Evans and Mrose(1955)' They also found one or more intermediate phases between mon-troseite and paramontroseite, similar to the weak phase referred to above,and suggested that the intermediate phase might be a partia[y dehydro-genated step between the two end phases. Klingsberg and Roy (1959)found an intermediate phase, which they named groutellite, to be formedin the reduction of ramsdellite to groutite, but not in the reverse reaction.

Their cell constants are given in Table 2; they are croser to those of theweak phase of the ramsdellite from Gavilan Mine than to those of rams-dellite proper.

The published *-ray powder patterns of ramsdellite give spacings ingood agreement,l except for one sample studied by Allsman (1955). Thestrongest l ines are l isted in Table 3, along with measurements for"Nsuta MnO2" and grouteil i te. It wil l be noted that the spacings given

I The patterns of 2 samples from czechoslovakia given by Bernardova and Sransky(1960) also are in good agreement with Nos. 1-6 of Table 3.

>.,- i : c€

= g = : 9 = ; - 3 ; 9 6- J d i O : J N N - j ? . 9

.f4 M. FLEISCHER, W E. RICHMOND AND H T. EVANS' JR

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RAMSDELLITD, ORTHORHOMBIC DIMORPH OF PYROLUSITE 55

for sample No. 7 differ distinctly from all the others and are very close tothose of the "Nsuta Mno2" of Sorem and cameron (1960) ; the materialis probably not ramsdellite.

The relation of ramsdellite to the synthetic compounds called gamma-Mnoz and rho-Mno2 and to the naturally occurring material calledNsuta Mnoz is a very important problem because of their extensive usein dry cell batteries. It is evident from the cell constants for these ma-terials, l isted in Tabre 2, that they are closely related, but the various in-vestigators have disagreed markedly on the nature of the relationship andthe details of the structure of gamma-Mnoz. No further discussion isgiven here; the problem is discussed with many references by sorem andCameron (1960), and new data are also given by de Wolff (1959), Nye etal. (1959), and Feitknecht et al. (1960). The Swiss workers formulategamma-MnO2, not as a defect structure, but as MnOz_,(OH),, with nranging from nearly zero to a maximum of 0.54, and find a straight line in-crease of total cell volume from nearly anhydrous gamma-Mno2 withincreasing n, which when extrapolated, falls close to the value for groutite(" : r ) .

Pnvsrcar, PnoppnrrBs

Ramsdellite is steel-gray to iron-black in color. The streak is given asblack by Fleischer and Richmond (1943) and by Klingsberg and Roy(1957), but Ramdohr and Franzel (1956) srate emphatically that thestreak is reddish. New trials on material from Lake valrey and GavilanMine showed that nearly all samples free of iron oxide gave a dull brackstreakl a few gave black streaks with a slightly brownish tint. The hard-ness is variable, 2-4, mostly about 3. specific gravities measured are4.73,4.65,4.83 (Lake Valley), 4.37 (GOzdrem, Turkey, Schrcider, l9S2);calculated from Bystr<im's r-ray data assuming the composition Mnoz,4.84. Cleavages on three pinacoids and a prism (Ramdohr and Frenzel,1956) commonly give the mineral the appearance in hand specimen ofoverlapping platelets; in polished section it commonly appears to befinely fibrous. Optical data in reflecting light are given by Ramdohr andFrenzel (1956) and by EI Shazly and Saleeb (1959).

OccunnBNcBs

Verified occurrences of ramsdellite are. U.S.A.: Lake Valley, SierraCounty, New Mexico; Monroe-Tener Mine near Chisholm, Minnesota(Klingsberg and Roy, 1957); Idorado Mine, Colorado (Kulp and perfetti,1950); Bannock County, Idaho (Allsman, 1955); Blythe, California;Canada, East River, Pictou County, Nova Scotia; Mexico, GavilanMine, Lower California; Czechoslovakia, Horni Blatna (platten) and

56 M. FLEISCHER,W. E. RICHMOND AND H. T. EVANS' TR.

Piebuz, Bohemia (Bernardova and Slansky, 1960); Turkey, Kodjas

Karil Mine, Roumelia, (Fleischer and Richmond, 1943), and perhaps at

Giizijrem (Schriider, 1952); Egypt, Yoider, Gebel To Yu, and Um Bogna

(EI Shazly and Saleeb, 1959); India, Dongri Buzurg and Sandur (Muk-

herjee, 1959). No doubt many more occurrences wil l be found'

The manganese deposits at Lake Valley have been described by

Creasey and Granger (1953). Ramsdell ite occurs in fissures and faults in

limestonel most of the samples came from a few pockets in the Stone

Cabin fissure, which is marked on their map. Most commonly it occurs as

groups of crystals (Fig. 5) on highly ferruginous chert; less commonly as

"nail-head ore" (Fig.6). Much of the ramsdell ite has inverted to pyro-

Iusite; portions of a single crystal may give the r-ray pattern of ramsdel-

Iite or of pyrolusite or of a mixture of the two.

Ramsdell's type specimen, from an unknown locality, is mostly mas-

sive, but partly platy; it occurs on a light brown chert distinctly different

from that at Lake Valley. The specimen from East River, Nova Scotia

(U. S. National Museum C1724) consists of fine platelets of ramsdellite,

entirely surrounded by coarse blades of pyrolusite. The specimen from

Blythe, California, is an irregular nodule approximately 3 by 2 inches,

with an outer rim I/16 to f inch wide of fine-grained psilomelane, the in-

terior consisting of a mixture of finely crystalline ramsdellite and pyro-

lusite.The origin of ramsdellite and pyrolusite as weathering products of

groutite and manganite, respectively, can be explained on a crystal

chemical basis as described above. Pyrolusite is recognized as the stable

form of MnOr and presumably can also be formed as a primary mineral

but it is possible that ramsdellite, like paramontroseite (see Evans and

Mrose, 1955), is actually metastable and can be formed only by the oxida-

Frc. 5. (Left) Ramsdellite, group of crystals, Lake Valley, Nerv Mexico.

Frc. 6. (Right) Ramsdellite, "nail-head spar," Lake Valley, New Mexico'

RAMSDELLITE, ORTHORHOMBIC DIMORPH OF PYROLUSITE 57

tion of groutite. The apparently universal presence of pyrorusite in vary-ing amounts disseminated in ramsdellite in oriented position suggeststhat ramsdellite undergoes further, slower (reconstructive) alteration topyrolusite as the more stable phase. Ramsdell ite has not so far been ob-served in a mineral association that would suggest it to be of primary oc-currence, that is, deposited directly from mineralizing solutions. There isas yet no evident clue in the observed occurrences as to the specific condi-tions that cause the formation of manganite rather than groutite and viceversa' Further attempts to synthesize these compounds are desirable.

AcruowrrpGMENTS

we are indebted to our colleagues s. c. creasey, who colrected the sam-ples from Lake valley and gave us data on the occurrence, K. J. Murataand Nancy M. Conklin for spectrographic, Charlotte M. Warshaw forchemical, and J. M. Axelrod ior x-ray analyses; to L. S. Ramsdell wholoaned us his type specimen, and to J. A. Noble for the gift of the samplesfrom the Gavilan Mine. The photographs were made by Anthony M.Denson.

RnrunnNcnsAr,r,sue'r, P' L. (1955), oxidation and enrichment of the manganese deposits of Butte,

Montana. Thesis, Montana School of Mines. o. l-93.Benne'ruova, E. ,rNo E. Sr,tNsr<v (1960), The o..or."n." of ramsdenite in czechoslovakia.

V es tnik u slr ed.. ustaau geol,., 35, 1 53- 1 54 (Engl. summ. ) .Bvsrndu, A. M. (1949), The crystal structure of ramsdellite, an orthorhombic modifica-

tion of MnOz. Acta Chem. Scand., 3, 163-17 3.carr,r.inn, srlroNNa axn Fn.rNcors Knaur (1954), comportement thermique de quelques

min6raux manganesif eres . A c oit. S ci. p ari s, C om b tr. r end. 23g. 2g6_2g7 .Corr, W. F., A. D. Wnoslev, a*n A*eN Wer-xrrv (1947), An r-ray diffraction study of

manganese dioxide. Trans. El.ectrochem. S oc., gZ. 133-154.Cor.r,rx, R. L. .q,No W. N. Lrpscoun (1949), The crystal structure of groutite, HMnOz.

A cta Cr ys t., 2, 10+-106.Cnnasrv, S. Q. exo A. E. GnaNcrn (1953), Geologic map of the Lake Valley manganese

district, Sierra County, New Mexico. LI. S. Geot,. Suyztett Mineral Inl. Fielit Stuilies) [ap,MF9.

Er. Sgazr,v, E. M eNr G. S. Sar.Bns (1959), Contributions to the mineralogy of Egyptianmanganese dep osits. Econ. Geol.,54, 873-ggg.

Ev.tNs, H' T., Jn. am M. E. Mnose (1955), A crystal chemical study of montroseite andparamontroseite Am. MineraL, 40, 861-875.

Fnrrxrvncur, W., H. R. Oswem, am U. Fnrrr<NscHr-STETNMANN (1960), Uber dietopochemische einphasige Reduktion von 7-Mnoz. Helo. chim. Acta.4J, lg4l-lgso.

Fr,trscran, Mrcnanr, (1943), Determination of active oxygen in the presence of barium andlead. Ind.. Dng. Chem., Anal. EiI., tS, 31-32.

--- (1944), Mineralogy of the manganese oxides. Application to problems of dry cellbatteries. U. S. Geol,. Surt:ey, (Mimeographed) 12 pp.

--- AND w. E. RrcrnnoNo (1943), The manganese oxide minerars: a preriminary report.Eco n. G eol, 43, 269-286.

58 M FLEISCHER, W L. RICHMOND AND II. T. EVANS, ]R.

GnuNrr, J.W. (1947), Groutite, HMnOz, a new mineralof the diaspore-goethite group.

Am. Mineral'., 32, p. 654-659.

Knnnsov, H., G. Kerz, aNo S. B. Lnvrr (1957), Structural relationship between ramsdel-

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Manuscript receitetl March 17, 1961.