Tn n AMERTcAx M rNERALocrsr]OURNAL OF TIIE MINERALOGICAL SOCIETY OF AMERICA

VoI. 20 FEBRUARY, 1935 No. 2

THE LINNAEITE GROUP OF COBALT-NICKEL-IRON-COPPER SULFIDES

W. A. Tenn, []niaersity of Missouri.

The linnaeite group of sulfides as given by various mineralogistsincludes several difierent minerals. Danal includes linnaeite(siegenite), daubr6elite, cubanite, and carrollite. He does not in-clude polydymite. In the 1932 edition of Dana-Ford's Tertbook ofMineralogy (pp. 430-431), sychnodymite is included with linnaeite,and polydymite is called "nickel-linnaeite." Violarite and badeniteare also placed in this group. It may be possible that later studieswill place badenite, (Co,Ni,Fe)3 (As,Bi)a?, and daubr6elite,FeS.Cr2S3, definitely in this group, but cubanite, Cu2S FeaS5,does not belong here as it is orthorhombic in crystallization.Doelter2 uses the term "Polydymite-Carrollite-group" for thelinnaeite minerals. Linnaeite (siegenite), polydymite, carrollite,and sychnodymite are included in his list. Daubr6elite is placed inthis group, but not because Doelter is satisfied that it belongsthere; he merely follows the grouping of other mineralogists.Hintzes includes carrollite, daubr6elite, linnaeite (siegenite), sych-nodymite, polydymite, and also hauchecornite, which, however,as it crystallizes in the tetragonal system is not a member of thisgroup. Violarite, (Ni,Fe)3Sa, was described and named by Lind-grena (who without an analysis tentatively assigned it the formula,NiSz), and is undoubtedly a member of the linnaeite group. Theformula, (Ni,Fe)35a, was determined by Short and Shannon(Ref. 31) in 1930. The following minerais are included in this dis-cussion: linnaeite, carrollite, sychnodymite, siegenite, violarite,and polydymite. Daubr6elite, the iron-chromium sulfide, includedin the linnaeite group by some mineralogists, will not be discussed

1 Dana, E. S , System oJ Mi.nerology,6th Edit., 1909, p. 78.2 Doelter, C., Hand.buch d.er Minerolchemie, Band iv, pt. I, 1926, pp. 645-657.3 Hintze, Catl, Hand,buch d.er Mineralogie, Band I, pt. I, 1904, pp. 957 968.a Lindgren, W., Econ. Geol., voI. 19,1924, p. 3O9.

70 TEE AMERICAN MINERALOGIST

in this article because it has not been definitely shown that itbelongs in the isometric system. The proximity in the periodictable of chromium to cobalt, nickel, copper, and iron would favorthe possibility that daubr6elite would be found to be a member ofthe group; but r-ray studies are needed to determine its structure.

The marked range in composition shown by the minerals withinthis group was brought to the writer's attention while he was com-paring a new analysis of siegenite with the earlier analyses of themineral. The new analysis was made in t932 by Lixb of a siegenitefrom the well known Mine La Motte locality in Madison County,Missouri. The analysis was made on crystals carefully selected soas to be practically free from chalcopyrite, the commonest andmost intimately associated mineral. This analysis is number 28 inthe list given below. Mr. Lix after studying a group of analysesplaced his new one among those of the siegenites. He concludedthat the cobalt, nickel, iron, and copper determined in his analysiswere isomorphous, a conclusion in accord with that made by someothers who have studied the group. This study has been made bythe writer in an effort to determine whether these four elementsare actually isomorphous, and whether dividing lines actually existbetween the minerals within the group.

Each mineral of the group is fairly well represented by analyses,which, however, as would be expected, vary in their completenessand accuracy. After eliminating those of manifestly little value,there remained 37 analyses (one of them a recalculated analysis).These are tabulated in the order of their decreasing cobalt con-tent, and under their common mineral names in the following table:

LrNNnBrrB (Haidinger, 1845)

1234

67

1 2 . 2 5+t tu43 5641 .834t 4342 7642 t9

53 3548.7048 6344.9240.7139. 3s3 9 . 3 3

4 . 7 5Trace0 . 1 9/ .tJ

14 09t 2 . 3 3

2 . 3 02 . 3 63 . 5 54 t 91 . 3 01 0 64 . 2 9

0 . 9 72 . 4 04 4 38 . 2 28 . 7 9t . 6 l2 . 2 8

R:Srratio

RaSl osRrS: eeRrSo ,zRrSl oaRsSl rgRrSn rtRrSs go

Locality

MiisenCarroll Co , NId.Sykesville, Md.BastndsGladhammarMiisenGladhammar

5 Lix, Henry W., The Composition and Occurrence of Siegenite. M.A. 'Ihesis,

Unir. oJ Mo.,1932.

Num-ber

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 7I

Localitl'RrSrratio

8o

101 112I J

14l . )

t6r7

Carroil Co., Md.CarroII Co., Md.Carroll Co., Md.Carroll Co., Md.KantangaGladhammarCarroll Co., Md.Carroll Co., Md.GladhammarGladhammar

Siegen I.Siegen I.Siegen I.

Julian, Calif.Sudbury, Ont.Sudbury, Ont.

MiisenMineralHill, Md.MiisenMiisenMine La Motte, Mo.Mine La Motte, Mo.MiisenMine La Motte, Mo.HilgenrothMiisen

41 344 1 7 l40 -9440.9939.4039. 894l 934 1 . 8 939.4740.74

SvcrrNooyumn40.6440.3339.28

StnceNrrn42.6339.7040.4041 .9842 t34 t . 5 4+0.6142.43J / O O

42 30

4 2 . + 23 8 . 7 038 2137 .6537 5037 29s7 2536. 0835 .3035 15

(Laspey

35.79. J5 . 04

26.80

(Dana,26 .082 5 . 6 923 392 2 . O 921 672 r . 3 42 0 M2 0 . 3 616.4711 .00

Trace1 7 01 5 4t . .)+

Trace0 . 7 81 5 47 6 5r . / o7 0 r

res ,18913 . 6 65 7 +5 . 7 0

18so)3 1 . 1 829.562 7 . 7 833.6431 .0030. 5338 1631.242 6 . 5 54 2 . 6 1

0 . 2 80 -461 5 51 . 4 0

2 5 4t 2 62 2 52 3 32 1 8

0. 930 . 8 23 . 8 6

0 . 6 2r 9 62 9 82 2 93 . 4 2. J . . J /

0 5 73 . 2 29 . 0 24 . 6 9

19.33t7 .o rr5 47

rll,+ .7 64 1 23 8 43 .98

rJ .4 .1

17 55r7 7919 1819. 6019. 33t t . + 6

9 . 9 820 4213 90

1 8 . 9 8t 7 . 2 323.+6

2 . 2 3

Trace

3 . 1 60 . 5 7

RrSr

RrSl osRrSr gz

RsSs szR:S: coRrS, toRrSn rtRrSq reRrSr.z,RrSr ro

R:S: arR:Ss uRsSs zz

RsSl oaR:S:.zoRrSo onRrS* rsRtS, t,RsSl . rzRsSa zzR3Sl osRrS: szRsSn

1 81920

2 l222324252627282930

Vrorenrru (Lindgren, 1924)J I

. )z

JJ

34J . )

36

RsSe.grRsSr.o:RsSt.r,RaSa.ar

42.17 | 2 .so I 33 .e4 |41 .68 | 1 .0s I 38 .68 I41.3s I I

n ' tr ]

Por.ynvurrr (Laspeyres, 1876)

72 THE AMERICAN MINERALOGIST

RtR en eNcrs lon AN,qlvsrs

1. wernekinck, Leon H, ;;,H :T ;i#;:l*2. Shannon, EarI V., Am. Jour. Sc., vol. ll (1926), pp. 489-493.3. Shannon, EarI V., Am. Jour. Sc., vol. ll (1926), pp. 489-493.4. Cleve, P.T. ,Geol . F i i l . F i j rh. , vol I (1872), p. 125.5. Johannson, K., Arkit. Kemi, M in. Geotr. ; vol. 9 (1924), No. 8, 22 pp.6 RammelsberC, C F. , f our. prakt . Chem.,vol .86 (1862), p.343.7 Cleve, P. T., Geol Fiir. Fdrh., vol l (1872), p. 125.8 Shannon ,Ea r lV . , Am.Jow . Sc . , vo l l l ( 1926 ) , pp .489 -493 .9 Smith, L. , and Brush, G.1. , Am. Iour. Sc. , vol . 16 (1853), p. 367.

10. Smith, L., and Brush, G. J , Am. Jour. Sc., vol. 16 (1853), p. 367.11. Smith, L. , and Brush, G. ! . , Am f our. Sc. , vol t6 (1853), p. 367.12. de Jong, W. F., and Hoog, A., Zeits. Kryst,., vol.66 (1927), p. 168.13. Johannson, K., same as No. 5.14. Smith, L., and Brush, G. J., same as No. 9.15. Shannon, Earl V., same as No 2.16. Johannson, K., same as No. 5.17. Johannson, K., same as No. 5.18. Laspeyres, H., Zei,ts. Kryst., vol. l9 (1891), p. 19.19. Laspeyres, H., Zeits. Kryst., vol. 19 (1891), p. 19.20. Stahl, W., Zeits. Kryst.,vol.35 (1901), p. 289.21. Eichler ,A. ,Henglein,M.,andMeigen,W.,Centralb lat tMin.(1922),p.225.22. Genth,F. A. , Am. Jou.r . Sc. , vol .23 (1857), p. 419.23. Eichler, A. etc.. same as No. 2124. Rammelsberg, C. F., Mineralchemi,c, vol.4, supplement (184a), p. 118.

25. Genth, F. A., Am. Jour. Sc., vol.23 (1857), p.419. (Recalculated from 26leaving out Pb and insol.)

26. Genth, F. A. , Am. Jow. Sc. , vol .23 (1857), p. 419.27. Hage, Th., Mineral. Siegen (1887), p. 29.28. Lix, Henry W., Thesis., Univ. Mo.,1932.29. Wolf, G , Beschr. Bergrea. Hamm (1885),p.34.

.30. Rammelsberg, C. F., same as No. 24.31. Short, M. N., and Shannon, Earl V., Am. Mineral., vol. 15 (1930), pp. l-22.

For name see Lindgren, W., Econ. Geol., vol. 19 (1924), p. 318.32. Short, M. N., and Shannon, Earl V , Am. Mineral, vol. f 5 (1930).

33. Clarke, F. W., and Catlett, Charles, Am. Jour. Sc., vol.39 (1889), p. 373.

34. Laspeyres, H., Jour. Proh. Chem., vol. la (1876), p. 397.35. Laspeyres, H., Jour. Prah. Chem., vol. t4 (1876), p. 397.36. Laspeyres, H., Jour. Prah. Chem., vol. fa (1876), p. 397.37. Laspeyres, H., Jour. Prak. Chem, vol. 14 (1876), p. 397.

Most of the above analyses are more readily accessible in one of the following:

Doelter, C., Handbuch der Mineral chemie, voI.4, pt. | (1926), pp. 645-657,702(violarite).

Hintze, C., Handbuch der Mi.neralogie, vol. 1, pt. 1 (1904), pp. 957-966.Dana, E. 5., System oJ Mineralogy,6th Ed (1909), pp. 75-79.Mineralogical Abstracts of the Mineralogical, Society oJ Gredt Brilai.n.

TOURNAL MINERALOGICAL SOCIETY OF AMERICA 73

For the most part, the analyses of the minerals are fairly similar,allowing, of course, for the steady decrease in the content of thecobalt and its replacement by the other three metals: nickel, iron,and copper. The quantity of these three metals that replaces thecobalt varies rather widely, and in the past (with some exceptions)they have been regarded as impurities. The various formulae(in which R:Co,Ni,Fe,Cu) suggested for each of the differentminerals are as follows:

Iinnaeite-R:S+, CoS. CozSr, or CoCo:S*.carrollite-RaSr, CuS. Co2S3, or CuCozSr.sychnodymite-R3s4, R4S6, usually (Co, Cu, Ni)rSs.siegenite-R3Sa, usually (Ni, Co)sSr.violarite-RsSr, usually (Ni, Fe)rSr.polydymite-R3Sa, also NiaS6, (Ni, Fe, Co)aS5.

These various formulae were tested by recalculating all theanalyses for each mineral, and it was found that the formula ReSnwas the best. However, *-ray studies of the members of the group(save violarite) show that they have the typical spinel structureltherefore, their formula should be written R"Rz"'Sn (R//:di-va lent Co,Ni ,Cu,Fe; and R"/ : t r iva lent Co,Ni ,Fe) . The s im-pler formula might be used, but it seems better to use the one in-dicating the molecular structure of the mineral as revealed byr-rays. In the above table, the RsS+ was used because it indicatesbriefly how closely each analysis approaches the exact 3:4 rutio.It should be noted that only Co, Ni, and Fe are assigned placesin the trivalent group. This is in keeping with the chemistry ofthese elements as the compound RrSa is known for all of them.No similar salt exists for copper; therefore, when it occurs in thelinnaeite group it appears only with the R" elements.

An inspection of the table reveals five well defined groups ofanalyses, with a doubtful sixth if sychnodymite is recognized asa separate mineral because of its nickel content. At one end arethe dominantly cobalt analyses representing linnaeite, and at theother end the nickel-rich analyses representing polydymite. Thecopper-rich analvses without nickel are grouped as "carrollite";for those having some nickel, the name "sychnodymite" has beenused. The latter name would seem to be of doubtful value evenas a variety name, as the three analyses of it closely resemblethose of carrollite, with which it probably belongs. Where bothnickel and cobalt are present in somewhat similar amounts, the

74 THE AMERICAN MINERALOGIST

name ((siegenite" is used, and as the cobalt decreases and iron

appears with the nickel the mineral is called "violarite." It is

conceivable that there should be a mineral having the compositionFe3S4, corresponding to the similar salts of cobalt and nickel, but

none is known.Figure 1 presents graphically, and in the same sequence, the

composition of the analyses given in the table. The curves for each

Frc- 1. Curves showing the composition of the linnaeite group by elements.

Numbers are those of the analyses in the table.

element (assuming that cobalt is the dominant element) bring out

the relationship of the copper to the cobalt and nickel, and the

nickel to the cobalt and iron. That the copper is isomorphous with

the cobalt is shown by the increase in its content as the cobalt

content decreases, the two curves approaching each other steadily.

Also, that some nickel replaces the copper is shown by the increase

in the nickel content with the copper-content decrease. Where the

total amount of copper and nickel are plotted together, as in

figure 1, the character of the resulting curve matches nicely with

60

.10

s.so.xsr,I

-e, ZO

I Linnaeite I Cor.ol l i te

Ir t_1'u-t''l6.so,4lv '\J V' -

V * ,\.,'' \.-_I 2 t + t 6 ? E ? to tt,2 t3,#tt t3 t? tB n zo a 22 zt 2t 2t 2a 2? zt zt,o,t tz.! r(,s aLD

lx, i iti ' i"ii . ' IY 1

ii i'$'j

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 75

the changes in the cobalt curve. Where nickel entirely replacescopper and equals or exceeds cobalt in amount, as it does insiegenite, the nickel curve mounts steadily as the cobalt contentdecreases. Near the end of the series, iron enters and replaces apart of the nickel (Fig. 2), forming violarite; but at the end theiron has decreased until only nickel is left. Cobalt and iron appearto have little in common, as iron does not appear in any quantity

Frc. 2. The paired isomorphous elements: Co*Cu and NifFe, of figure 1.Note the strong similarity of the two curves throughout.

until the cobalt content has fallen below 10 per cent. The appear-ance of the iron in the nickel-rich members is in perfect keepingwith the common association of these two elements in many otherminerals. The copper undoubtedly takes the place of the cobaltin the R" position in the spinel formula. Cobalt is both divalentand trivalent, hence in linnaeite it appears in both formsl but, asthe copper enters, it displaces the cobalt as the divalent element.As both nickel and iron are also divalent, varying amounts of boththese elements may replace some copper and cobalt. A check of

A r-*'x

/ ' rC o , C u

l. /-"'t ;^'l

? i l t 3 t f t 7 t ? 2 t

I! t ' . Fi l v l r r e

II

t l

,x. i \.,'',' 'r.r

-{

$'5t r o

( 'tF

4 Q6 +Cu

A.\G4

2 ' 2 f 27 '? i t l l r t 375 7

t

i ' Fo

t l

THE AMERICAN MINERALOGIST

the percentage of copper in carrollite and sychnodymite showedthat in only one analysis did the copper content exceed the amountof copper (i.e., 20.52 per cent) that could replace the divalentelements. Johannson (Ref. 5) suggests 15 per cent as the maximumfor Cu in l innaeite, and regards carroll i te as a mixture (a needlessand erroneous deduction). Further evidence that the copper isisomorphous with the cobalt is shown in figure 2, in which total

Frc. 3. Curves based upon decreasing Cof Cu content. Note the positions of

linnaeite (L) and sychnodymite (S) with reference to the carrollite (C). The Co inpolydymite No. 34 is ignored in the arrangement.

cobalt and copper are plotted together as are total nickel and iron.Whenever the first two decrease, the last two increase. As thecobalt content controlled the distribution in the plotting, thematched irregularities in the two curves suggested that the orderof plotting in the curves should be according to the sum of thecobalt and copper. This was done for all the analyses, and a curveconstructed (figure 3) according to the decrease in cobalt andcopper content. This resulted in mixing the position of the first

cc cc cc L L L S L S L C C L L

AJ

S ' 30S.'

Uo\

^c, 20\

8 f? ! i 19 g to t | t t t+ | + i t c zzo 5 t? t i 7 3Ttz t78212 lz t2 !n 29 to r r 3 l r , ,11516,?

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 77

20 minerals (the first linnaeite analysis appears in position num-ber 11); in short, cobalt and copper are the determining factorsin the composition of linnaeite, carrollite, and sychnodymite,which strongly confirms the view that the two elements areisomorphous. The formula would then conform to that of thespinel group and should be written (Cu,Co)Co2Sa. This is in keep-ing with the chemical studies of Shannon,6 who showed thatcarrollite was similar to linnaeite and that copper, nickel, and ironwere also doubtless isomorphous with the cobalt.

The sharp change from the copper-bearing linnaeites to thenickel-rich siegenite indicates that the latter should be ranked asa species instead of being called a variety of linnaeite. The curvesindicate a fair uniformity in the composition of siegenite. Passingfrom siegenite to violarite, cobalt disappears and iron replaces itin the formula. Polydymite is at the end of the series and is anearly pure nickel sulfide, but still contains some iron and tracesof cobalt isomorphous with the nickel.

The relationships of the members of the group are perhaps moreclearly shown by figure 4 which is based upon the average analysisof each mineral (sychnodymite is averaged with carrollite). Thecurves for Co-lCu and for Ni*Fe show that as the quantity ofone pair of metals decreases it is accompanied by an increase inthe amount of the other two. Linnaeite shows a greater departurefrom the ideal CoaSa (indicated by X) than any member. Theanalyses show that all four elements are present. Carrollite closelyapproaches the ideal copper-cobalt sulfide, and polydymite doeslikewise for the nickel sulfide. The chemical affinities of the fourelements and the dominant isomorphous pairs are clearly shownby the curves.

This interpretation of the members of the linnaeite group as anexample of an isomorphous series of the four elements finds furthersupport in the *-ray studies which have been made of them. Thestatement is made in the 1932 edition of Dana-Ford's Tertbookof Mineralogy (page 430) that "n-ray study shows practicallyidentical structure in linnaeite, polydymite and sychnodymite.Structure is face-centered cube." Studies made by de Jong andHoogT show that carrollite has the same spinel structure as

6 Shannon, Earl V., The Identity of Carrollite with Linnaeite, Am. fou.r. Sc.,vol .2 l l , 1926,p.488.

7 de Jong, W. F., and Hoog, A,., Zeits. Krist., vol.66,1927, pp. 163-71.

78 THE AMERICAN MINERALOGIST

Iinnaeite and sychnodymite, which definitely correlates it with theother members of the group. Holgersson8 definitely added siegeniteto the group by his *-ray studies in 1929. Thus, the only mineralof the group not definitely shown by *-ray analysis to possess the

Frc. 4. Average analysis of the five major members of the linnaeite group(sychnodymite is averaged with carrollite, where it belongs).

spinel structure is violarite, and its composition strongly indicatesits possessing it.

The atomic radii of these four elements are so close that iso-morphism should be expected. According to Neuburger9 they are,in Angstrc im uni ts , Fe:1.259, Co:1.256, Ni :1.243, Cu:1.275.

8 Hoigersson, Sven, Chem. Zentr., vol' l,1929, pp.372-3.e Neuburger, M. C., Gitterkonstanten fiir 1931, Zeits. Kri.sl., vol. 80, 1931,

pp.126-127.

Wyckoff, R. W. G. has similar data in the second edition oL his The Struoture

of Crystals,1931, pp. 192-193.

i:$$I

I

I

i(o/ . rrS

II

i-i\

_ - I60

50

t0

3' So{cIJ(,

(, 20

lo

o

JOURNAL MINERALOGICAL SOCIETY OF AMERICA 79

These values would make it possible for them to replace eachother within a crystalline structure. The analyses show, however,that such replacement has been restricted dominantly to certainpairs, with copper and iron the subordinate elements. The doorwas open for an extremely variable group of replacements, which,for the most part, were restricted to these paired groups, indicat-ing that either the composition of the solution (in which one ortwo elements predominated) was a controlling factor, or that iso-morphism is a last resort in mineral formation. The fact that themineral members of this group occur alone favors the first inter-pretation.

However,l0 recent studies of the spinel structure by Barth andPosnjakll have revealed the fact that there are two structuralarrangements within the true spinel group, one with fixed positionsfor the ions and the other with variable positions. In the latter(for which Barth and Posnjack suggest the term, "cells withvariate atom equipoints"), "difierent atoms may partly replaceone another in structurally equivalent positions of a crystal."The fixed spinel structure corresponds to XYzSa(R"Rz"'Sn) in thelinnaeite group, and YXYSa is the arrangement in the variateatom equipoint group. As noted above, the study of the availablechemical analyses of the members of this group favored the formulaXY2S4 as being best suited to the chemical relationships of thefour elements (Fe,Co,Ni,Cu). The study showed, also, that theatomic radii would permit any element to isomorphously replaceanother. It is, of course, perfectly possible to apply the typeformula of the variate spinel group to this group of sulfides butthere does not appear to be any reason, at present, for doing so.II x-ray studies showed that violarite, for example, belonged inthe variate group, its formula would be written NiFeNiSa insteadof FeNizS+. Nothing seems to be gained by this change. Thelinnaeite group would seem to offer an excellent opportunity tomake an c-ray study of the sulfide members of the spinel group,and to determine, if possible, whether the two spinel groups are

r0 The writer is indebted to Dr. George Tunell of the Geophysical Laboratoryfor calling his attention to the new interpretation of the spinel structure and for sug-gestions as to its application to the linnaeite group.

11 Barth, Tom. F. W., and Posnjak, E., The Spinel Structure: An Example ofVariate Atom Equipoints: Jour.Wash. Acod. Sci.ence, vol. 21, 1931, pp. 255-258.

Barth,Tom. F.W.,and Posnjak, E., Spinel Structures:With andWithoutVariateAtom Equipoints: Zei.ts. Kri.st. (A) Band 82, 1932, pp. 325-341.

80 THE AMERICAN MINERALOGIST

present. Dr. Tunelll2 expressed himself regarding such a study asfollows: "On looking up the scattering powers of copper, nickel, andcobalt I find that they are so nearly alike that it will not be possibleto discriminate the two structure types in compounds of theseelements."

Dr. Wyckofi of the Rockefeller Institute for Medical Researchhas also expressed the opinionl3 that the "distinction (of the twoclasses of spinel structures) would have no bearing on the struc-ture of linnaeite considered basically as Co3Sa." These two opinionsindicate that as far as the minerals included in this study areconcerned, the fixed spinel type may be adopted as their struc-tura l tYPe'

Sunrunnv

This study of the chemical composition of the best analysesavailable for the various members of the linnaeite group hasfurnished, it is believed, evidence that all members of the groupshould be represented by the general formula R"R2"'Sa. The fourelements Co, Ni, Fe, and Cu are isomorphous, but copper, only,as a divalent element. The atomic radii of the four elements areso nearly identical that such isomorphism is easily possible. Thename "Carrollite" (CuCozS+) is preferred for those minerals richin copper, and "Sychnodymite" might very well be dropped, evenas a variety name. X-ray studies of all the members, exceptviolarite, show that they have the spinel structure type, and givefurther proof that the several minerals in the group: linnaeite,carrollite (sychnodymite), siegenite, probably violarite, and poly-dymite have the same type formula. It appears doubtful whetherfurther r-ray studies would contribute any more informationregarding the structures of the group.

D fn a letter to the writer.13 fn a letter to the wriler.