Tnn Amertcan M Rneralocrsr JOURNAL of the MINERALOGICAL SOCIETY of AMERICA

Tnn AmERTcAN M rNERALocrsr JOURNAL OF THE MINERALOGICAL SOCIETY OF AMERICA

Vol. 19 DECEMBER, 1934 No. 12

THE STRUCTURES OF VERMICULITES AND THEIR COLLAPSE BY DEHYDRATION

JonN W. GnuNnn, Uniaersity of Minnesota. INrnooucrroN The question whether vermiculites are distinct minerals has puzzled mineralogists for many years. A number of attempts have been made to find definite type formulas for them. Often they have been consideredas "hydrated micas." It will be shown in the following pagesthat this idea comesvery close to the truth, and that a vermiculite is a defi.nite mineral specieswith a definite crystal structure. If , however, a so-calledvermiculite contains alkalies to an appreciable extent a type of mineral results which is neither a vermiculite nor a mica but an "interstratification" of unit layers of these two. The r-ray dia"gramsfor this type are different from either of the other two. Preliminary and. necessaryfor the investigation of the vermiculites was the knowledge of the structures of the micas as de- scribed by Pauling,l and Jackson and West;2of the chlorites by Pauling3 and McMurchy;a and of the kaolin group by the writer'5 The structures of talc and pyrophyllite, suggested by Pauling6 and lately worked out by the writer,Twere also of great importance in the correct interpretation of the vermiculites. In obtaining material lor r-ray analysis the writer is especially indebted to Dr. C. S. Rossof the U. S. GeologicalSurvey, and Dr. W. F. Foshagof the U. S. National Museum who suppliedmost of the specimenslisted below.

l Pauling,Linus, Proc. Nat.Acad'. Scl., vol. 16, pp. 123 129' 1930. 2Jackson, W. W., and West,J., Zeit.J. Kr'ist.,vol. 76, pp.27l-227, and vol' 85, pp. 160-164,1933. 3Pauling, Liuts, Proc.Nat. Acod.,Sci.,vol. 16, pp' 518-582,1930' al\{cMurchy, R. C., Zeit.f . Krist ,1934, vol. 88, pp. 420 +32,1934. 6 Gruner,J. W., Zeit.f. Krist., vol.83, pp. 75-88, 1932;voI.83, pp' 393-404, 1932;vol.85, pp. 345-354,1933. 6Proc. Not. Acod..Sci.., vol. 16, p. 126,1930. 7 Zeit. J. Kri,st., 1934,vol. 88' pp. 412419, 1934. JJ6 TEE AMEMCAN M IN ERALOGIST

Crrourcar, Dara

The following twelve specimenswere examined. Their chemical analyses are given in Table I.

SpecimenNo. 1. Verrniculitefrom Bare Hills near Baltimore, Md. E. V. Shannon: Atn. Jour. Sci,., voI. 15, p. 21, 1928.pale yellow-greenscales resembling talc. CatalogueNo. 95647of U. S. Nat. Museum. No. 2. "Protovermiculite,'from Magnet Cove, Ark. F. W. Clarke and E. A. Schneider:Am. Jour. Sca.,vol. 42, p. 242,1891.Large goldenyellow booksor scales.Only very little exfoliation.Sp. grav.:2.05-2.10. No. 3. "Lucasite" from Corundum Hill, North Carolina. Th. M. Chatard: t/. S. Geol,.5,n., Bull.42, p. 51, 1887.yellowish brown, scaly. Catalogue No. gg507 of U. S.Nat. Museum. No. 4. Vermiculite from Wiant's Quarry near pilot, Md. C. S. Ross,E. V. Shannon and F. A. Gonyer:Econ. Geol.,vol.2Jrp. S42,1928. yellowish brown, compact, scalyaggregate. Talcose feel. Sp. grav.:2.31. No. 5. Vermiculite from Webster,North Carolina.Id,em, p. 536,Table 3, Analysis4. Greenishyellow scales. No. 6. Verrniculitefrom Webster,North Carolina.klem,Table 3, Analysis 1. Fine, greenishyellow scales. No' 7. Nickeliferousvermiculite from webster, North carolina. c. S. Rossand E. V. Shannon:,42r.Mineral,ogi.st, vol. ll, p.92, 1926.Apple green, small scales. Cata_ logue No. 95487of U. S. Nat. Museum. No. 8. "Jefferisite" from Brinton euarry, West Chester, pennsylvania. F. W. Clarkeand E. A. Schneider:Am. Jour.Scl., vol.40, p.4S2,Ig9}.Brownishblack Iargeplates. Sp. grav.:2.35. Exfoliates easily. No. 9. So called "vermiculite" from Libby, Montana. commerciar analysis by U. S. Bureauof Standards,Washington, supplied by C, S. Ross.Very dark green- ish brown scales.Sp. grav.:2.64. Exfoliatesreadily. Note the discrepancyin the analysesof the alkalies. No' 10.so carled"vermiculite" from unknown locality. Brownish black largeplates. Sp. grav.: 2.49.Exfoliates easily. No. 11. "Chloritic vermiculite', from Old Wolf euarry, ChestnutHill, Easton, pa. Describedby G. P. Merrill in Tl. S. Geol.Sunt., BuJl,.90, p. 19, 1g92.Light yellowish green, scaly, talc-like. Does not edoliate appreciabry. catalogue i.Io. ' 70118of U. S, Nat. Museum, No' 12. "verrniculite" from corundum Hill Mine near Franklin, N. c. unanalyzed. collected by c. s. Ross. Brownish to greenishblack Iarge scales.Harder than other vermiculites.

Additional information including optical data for these minerals may be found under their respective references. As in the micas the chemical analyses differ considerabry. Based ol tr ray diagrams specimens I to 7 belong to the same species which is here designated as aermicurite. specimens 9 and 10 belong to a species for which the name hydrobiotite is proposed. This name TOARNAL MINERALOGICAL SOCIETY OF AMERICA 559

F S8 E R:K e oo 6 NO: +o

H E o @

do9++< N+ o o€otsDN oN 300Noo ao o oi

l* €6bN 6e o lb otso- tso z 60 0 H lo 9NoN E lsN a H N A+N O+ q 9q1H e1 qN

5 $FG g € H sBg z d :*d 8*B E

tr 3

! I B

e-Ets: Te ddeqse???e?3 bb I iaa,;;,2>>a9z: A-; E Fr 560 THE AMERICAN MINERALOGIST

was used long ago by Schrauf8and others to designate biotite_like material high in water. Specimen No. 8 is a mixture of vermiculite and hydrobiotite since it gives both r-ray patterns. rt will be observed that it contains 2/6 alkalies and less HzO than typical ver_ miculite. No. 11 from Easton,pa. cannot be classifiedarpresent, it has no characteristic vermiculite lines and may be a mixture of talc, chlorite and serpentine.No. !2 is a distinct mixture of biotite and vermiculite as it gives both diagrams.

Tasrn If

Average of Theoretical analyses 1 to 7 compositions

sio2 35 04 35.04 36.7t:22 SiOz Al203 14.55 14. .').) 14.15: 5Al:Oa FerOs 5.13 5.13 4 43: FezO: FeO o.sel Nio -'^^lt ttl Mgo 21.711 25.20 24.62:22 MsO CaO 0.46) HzO 19.99 19.99 20 09:40HrO

Total 99.91

To arrive at a working formula for vermiculite anaryses1 to 7 were averaged as shown in Table II. This formula has to be accom_ modated in the structure which as shown later consistsof mica units, minus KzO plus HrO. Without the H2O the structural formula would be (OH)rMga(SisAl)Orodisregarding valencies.Re_ membering that Fe may replace Al or Mg, or both, and that more than 25/6 of Si may be replaced by Al the structural formula in_ cluding H2O may be expandedto (OH)r(MB,Fe)a(Si,Al,Fe)aO16. 4HzO; or written in a difierent form, it becomes: 11(Mg, Fe)O 3(Al, Fe)2O3.11(Si,Al)Or . 20H2O,or 22MgO 5AlrO3. FezOs. 22SiO2.40HrO. The amount of HrO in this formula is based on the average H2O content in Table II. The fact that the number of HrO molecules in this analysis is an even whole number makes it fairly certain. from the structural point of view, that it is correct. This formula is,similarto that proposedby Rossand Shannonewhich is 12MgO . 3Al2O3. 12SiO,.79+HrO. 8 Schrauf, A., Zeit. J Krist., vol.6, p. 3g1, 1gg2. e Am. Mineralogist, vol ll, p.92. 1926. TOTTRNAL MINERALOGICAL SOCIETY OF AMERICA 561

It is, of course, obvious that K+ cannot be removed from a mica and HzO substituted without having negative charges left over' These must be neutralized either by oxidation of Ferr to Ferrr or by introduction of H+. Another possibility would be the substitu- - tion of F- or OH- for O.- Which of these processesare operative is impossible to say at present. Usually there will not be enough Ferr present whose oxidation could neutralize the loss of K. It is commonly thought that Ferrr occupies Al positions. This is not so likely in the vermiculites for the Al occupieschiefly Si positions in the SiaAl Oro layers. The Ferr is in Mg positions to begin with. There is no reason why Fe on oxidation should move into Al positions. There would be no vacanciesanyway. The hydrobiotite analyses,9 and 10,and 8 which is partly hydrobiotite, contain considerable amounts of alkalies. The r-ray diagrams show clearly that these minerals are made up of interstratified single or double layers of units of mica (M), and vermiculite (V). The interstratifications which exist in them can be at least two-fold both agreeing with *-ray data. They are: M-V-M-V- and V-V-V-M-M-V-V-V-M-M-. Other combinations of these layers are possiblebut become complicated. The formula for the first one would be: (OH)aK(Mg, Fe)6(Si,Al, Fe)sozo'+IIIO' X-nav Dare On account of the physical nature of the material the powder method was used exclusively. Grinding of the samples in agate mortars distorted the structural planes to such an extent that no satisfactory diagrams could be obtained. All the sampleswere filed, therefore, unless received in crushed form, and screened through bolting cloth. The powder was mounted on silk thread with collodion. The thicknessesof the samples did not exceed 0.7 mm' A goniometer head was used for centering the samples in the cir- cular camera (radius:57.3 mm.). Cu radiation was found to be unsatisfactory on account of its marked a\qorption by minerals containing iron' Fe radiation (K":l'9321A) was used instead' It gives very satisfactory results with suffi-cienttime of exposure' AIso, with the arrangement used for minimizing fogging by the zerobeam it was possible to record the reflections of planes with spacings greater than d,:t+4. fnls is essential since reflections of planes with large d. are of.greatest importance in interpreting the diagrams. A self-rectifying gas tube with an output of about 7 to 9 Ma at 35 Kv was used. TH E A M ERI CA N M I N ERA LOGI ST

Tnerr flf. Pownnn Dracnaus

13.44 8 rc.74 /.UJ I 4.75 1 4.68 I 4.45 TX 4.41 0.5i 4.43 Ti 4.43 2i 3.91 1 3.88 tx 3.91 1 .t . .).t / 4 3.537 3.548 3 3.541 4 J, lzo I 3.129 0.5 3.104 1 3.137 1 2.838 2.838 3 2.852 3 2.840 ( 2.6 IX 2.630)r 2.630 I 2.620 2 I 10 2.521 2b 2.5s5) Lo 2.526 lb 2.530 2b 11 2.366 4 ) ?7< 2.375 2.372 4 t2 2.256 0.5 13 2.192 1 2.182 0.5 2.193 2.192 I 14 2.129 0.5 15 2 069 n( 2.052 I 2.068 2.068 I l6 2.035 I 2.038 2.033 I t7 2.002 0.5 2.002 lb 2.000 2.005 I 18 1.833 1 1.816 n( 1.836 1.836 1 19 1 20 1.732 0.5 1.732 0.5 1.733 0.5 1.730 I 2l 1.664 2 r.657 tb 1.668 3 t.670 22 1.584 0.5 I. JdJ 0.5 1.588 0.5 23 t.570 05 | .571 1 1.573 1 ai 1.526 1.530 4b 1.527 3b 1.526 6b

25 r.496 1 1.500 0.5 26 1.462 05 1.465 0.5 17 1.441 1.432 tb 1.Ml 2 1.445 2 28 1.429 I 1.428 1 1.433 I 29 r.352 1 1.348 0.5 1.354 0.5 1.353 I 30 1.321 3 1.328 3 1.330 3 31 1.312 1 1.314 2 o.b. 1.314 1 32 1.289 I 1.290 0.5 1.291 I JJ r.270 1 1.271 0.5

Spacing ofdoot: 28.42

i:indistinct edge of line. b: broad line. a.b.: very broad line. 0 - a line produced by Kp radiation of iron. JOURNAL MINERALOGICAL SOCIETV OF AMERICA 563 oI. VERMICU]-ITES. FE RADIATION

Indices

13.7A 13.64 10 13.64 10 002 7.0+ 0 7.r2 5 004

4.71 I 006 4.48 ti 4.39 I 4.+5 2b 3.90 I 3.92 I 3.94 tb 0088 3.540 3. 548 3.562 008 3.126 I 3. 145 1 3.L62 0.5i 00108 2.833 4 2.847 5 2.847 ti 0010 )r ]3;0,202,L32,200 and 2.609 2 2.6 l.-. I t t.o. r36p,204p lr 2.524 3b 2.537 r v.o. 2.48 JJ 132,204,134,202

2.367 4 2.379 3b 2.380 tb 136,204 2.253 0.5 t36,208 2.185 1 2.188 lb 206,138 2.059 1 2.069 1 20m,138 2.035 I 0014 1.998 2.002 1 13T0,208 1.828 1.833 I t312,2010 0016 1 1.735 1 1.739 0.5, 3b 1.668 2b t.676 2i t3T4,2ol2 l3l6p,20l8p 1.569 u.5 0.5b 0018,1314,2016 1.524 5b 3b 1.526 6b 060, 332, 330, 334, 1316,2014 1.498 0.5 0.5 1.494 2b 332,336

t.439 2 1.442 1 t.Ml 1316,2018 1.425 I t.429 I 0020 t.349 0.5 1.354 0.5 338,3312 1.32+ 2 t.329 3 13t8,20'f' 1.312 1.316 1

1.288 I t.292 1 1.300 0022 t.268 1 1.276 0.5,

28.38 THE AMERICAN MINERALOGIST

Table III contains the powder diagrams of the seven vermiculites. Lack of space does not permit the giving of distances meas- ured in mm. in the films and their corresponding @ angles. fn- tensities 1 are estimated visually. No correction except for thicknessesof sampleswere applied. On account of a slight-eccentricity of the camera, and other factors, readingsabove 3.0A are not as accurate as below that figure, especiallyis this true if they approach the zero beam. For the calculations of the unit cells only planes with d, smaller than 3A were used. These are quite accurate as found by comparison with standard substances.Some of the vermiculites give much sharper fi-ray patterns than others. The least satisfactory lines were found in nickeliferous vermiculite No. 7. Someof its lines could not be recordedwith certainty. T.q,sroIV. Poman Drncneusol. MrNnn.lrsFonmnrv DBsrcwemons Vnnurcurrres

In- dices

'*i;[; 002v 002or o05h J 002m i 6.93 8 004c and V 5 6 4.47l1 14.s0 4.48 4.47 2i 7 3.95 2p 008 0c 8 3.53 l3 13.56 3.55 7 008 7 and c J ,+Z 007 or ootS h 3.29 a 006 m .1.143I 0. 00108 v 12 3.071i 0.5 3.066 1 006 t TJ 2.919 0.5 t4 2.8731rp2.859 r0v l.) 1 l6 2.601 2.619 2 1.7 2.ssl| 2b ,n 18 2.s35| 0.5 19 2 434 + t andc 20 2.3?,4 3 b 2.391 z JOURNAL MINERALOGICAL SOCIETY OTI AMERICA JO)

T.ler-E IV (Conlinued)

12. 9.

d I dlI

2l 22 2.2560.5 2.220to 23 2.173 LO 2.1662b 2+ 2.075 I 25 2 005 2b 2.016 z 26 1.918 0.5 27 1.836 0.5pr.8,420.sB 23 29 30 t.734 I 1.7340.5

JI r.670 3b 1.6683b 32 1.5660.5 7 33 r.s2+ls 1.533J

34 1.5170.5 JJ 1.443 I 1.437 36 1.429 1

J/ 1.401 nq 38 1.357 1 t.3+6 0.5 3S 1.328 z 1.3223 40 1.315 I 4l 1.292 I 1.298I Spac-]28.38 28.50 23.7to 24011'll ing of and and t+.2 iloorLnn 124.0 20.02

7 : reflection of vermiculite. &: reflection of hydrobiotite. m:rcflection of mica. l:reflection of talc. c: reflection of chlorite.

Since these minerals are certainly composed of layer structures similar to the micas and chlorites, the possible reflections from the basal planes should be rather prominent and easily identified. This is the case as may be seen in the tables III, IV, and VIL These reflections are especially sharp and conspicuouswhen the samples are mounted on thread because the cleavage particles align them- selves parallel to the thread and give observed intensities 3 to 4 566 THE AMERICAN MINERALOGIST times as great as calculated. This was explained by the writer in a paper on dickite.lo It is a curious fact that the r-ray diagrams of powders heated to 110'C. lor 24 hours do not show any changes,though very considerable amounts of water are driven ofi at 110o C. as shown in Table L Specimens7,2 and 10 were r-rayed after this treatment. Heating for 5 to 24 hours at 750oC. producesnew diagrams which are the result of the collapse of the structures in a direction normal to the basal cleavage. INrn'nrnprarroN or, X-nay DATAor vERMrcutrrE The first step in the interpretation of the diagrams was to com- pare them with those of micas, chlorites, the kaolin minerals and talc. Certain striking similarities are noticed if the basal plane reflections are disregarded. No detailed account can be given of them in this place. Sufice it to state that the width Doof the unit cell of any of these structures is always given approximately by a strong line, examples, No. 24, Table III and No. 33, Table IV.l1 The dimension tl6 of the unit cell in the direction of the a axis can be computed from this reflection since the layer lattices are made up of hexagons.l2 Recalculations for greater accuracy of these dimensions are carried out after the indices for most reflections have been determined. The most important clue to the structure was found when it was realized that vermiculite on dehydration at 750' C. gave a diagram almost identical with that of talc as shown in Table V, which contains the talc diagram and its indices as far as it concerns the present discussion, the only differences are that the basal reflections and most of the others are more difiused and broader than in talc proper.l3 This great similarity is also noticed in other prop- erties of the dehydrated material. The scaly particles have a talc- osefeel and even look like talc in iron poor varieties. At this stage of the investigation the structures of talc and pyrophyllite were determined.la to Zeit. f. Krist., vol. 83, p. 395, 1932. 11 The distance d must be multiplied by 6 since the reflection 060 is the 6th order oI the plane 010; d. oI 010:bo. 12See papers on mica and kaolinite. 13 An explanation for this diffusion is to be found in the smaller grain size of individual particles after heating. They become too small for optimum reflective ra Op. cit. TOURNAL MINERALOGICAL SOCIETY OF AMERICA JO/

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TaIc consists of units like mica with the alkali layers absent as pointed out previously.l5 If vermiculite dehydrates to a talc-like structure no other layers but those made up of volatile material can occupy the positions that are filled by the alkalies in mica. Obviously this must be mostly or entirely water. With this information it is possible to determine the entire structure. How these calculations are made has been describedin previous papers.16 Agreement between theoretical and observedintensities is reached in vermiculite when the shift of one layer over the adjacent is approximately I/3 of the length of o6 (expressedin degrees:120") parallel to the o axis but in the opposite direction from the shift in the micas, chlorites and talc, as shown diagrammatically in Fig. 1. The resulting B angle is 97o09'* 10/. The atomic coordinatesare given in degreesin Table VI.r7 T.lsrn VL Aromc Coonorwarrsol C6:r,lon Vnnurculrrn. Foun Equrv.lrrr.rr Arous lon Eacn PosrrroN

Atom Atom

Mgt 0' 0" 00 Oo -58 30 138.5 Ms, 0 120 0 Oz 122 30 138.5 Mgt 0 -120 0 oE ?) 120 138.5 Or -51 180 t4 Oe 51 180 166 Oz -51 60 l4 Oro 51 60 166 OHr -51 -60 14 OH, 51 -60 766 o3 58 30 41.5 Str 143 0 34 Or -122 30 41.5 Si, -J/ 60 34 o6 -32 t20 41.5 Si3 -143 0 146 Sl4 J' 60 146

Table VII contains the calculated theoretical intensities of important planes as compared with the average of the observed intensities of the first six diagrams of Table III. The dimensions for calculating the distances of Table VII were taken from the chlorite structure and are: B:97"8'40", oo:5.314, bo:9.20h, co:28.464. The space group is C6za.The average dimensions of 15Gtuner, J. W., Am.Minerol,., vol. 16, p. 451and Fig. 22, 7931. n Zeit.f. Krist.,vol. &t, p. 79and p. 395,1932. 17 The space group relationship of mica and vermiculite, both in C %r,is this: The principal or para-glide planes (Paragleitspiegelebene, component: c/2) of. vermiculite are tlle clino-glide planes (component:c/2*o/2) of mica. The direction of gliding in vermicuiite difiers only by about 2!" fton that in mica in the same plane. TOURNALMINERALOGICAL SOCIETY OF AMERICA 569 vermiculites are slightly larger. For examplet co:28.664 on an average. Allowance must be made for these slight differences in comparing Table VII with III. Most interesting is the fact that the H2O occupiesa very definite thickness in the unit cell. This is shown by the figures at the Tlslp VIL Tsnonorrcer,exo Olsrnvnl fnrnNsrrmslon Two Morrcur.nsor' Venurcur,rrn.No Arr-ow.u+cnrs Meon roR THEGr-eNcrr.rc ANcr.e

'fheoret Theoreti- cal cal Intensit Intensity

002 t4.12 451 2014 1.707 0 004 7.06 2l r3T4 1.656 302 006 4.7r 13 2012 1.656 151 020 4.60 55 0018 1.569 34 008 3.530 lJ/ t314 1.559 69 0010 2.824 106 2016 1.558 130 2 650 25 060 I . J.tJ 205 202 2.650 t3 ??t 1.533 412 r32 2 63s 39 330 r.52+ 250 200 2.634 18 JJ* 1 \1L 164 132 2.576 102 1316 1.513 2r4 204 2.575 53 20L4 I. JIJ 103 r34 2.534 302 332 t.498 .t.') 202 151 JJO 1.498 36 134 2.432 28 1316 l.+28 405 206 2.431 13 20T8 t.428 203 136 2.374 45+ 0020 1.4r2 62 204 2.373 219 1318 1.389 0 0012 2.353 l3 2016 1.389 0 136 2.250 27 338 1.347 67 208 2.249 l4 JJIJ 1.317 61 138 2.186 2l+ 1318 t.3t+ 405 206 2.186 103 2020 1.31.4 20+ 138 2.058 92 0022 1.284 20T0 2.058 48 0014 2.Or7 104 1310 1.996 203 1.995 29 1310 1.875 t9 2012 1.875 11 13I2 1.8r7 103 2010 1.817 .)+ 0016 1.765 o 1312 1.707 0 570 THE AMERICAN MINERALOGIST bottom of Table III which give the heights of the unit cells meas- ured normal to the base.If a singlelayer of talc (:9.26L, the unit cell is double this height) is subtracted from a single layer of vermiculite (:I4.23b the thicknessof a water layer is found to be 4.974. Almost the same figure may be obtained by subtracting l ut it:- if- t!l

lstA I Vermrculite Ch/orrfe

------Biot'ile --- Tolc Frc. 1. Outlines of monoclinic unit cells of biotite, talc and chlorite superim- posed on that of three unit cells of vermiculite. Plane of paper parallel to axial plane a-c. the mica unit in chlorite from the chlorite :urrit(l4.l2ft-9.28A: 4.844). Therefore, the H2O layer requires a slightly larger space than the so-calledbrucite unit 6Mg(OH)2 in chlorite. Expressed in another form, V of 6Mg(OH)z:V oL 8H2O in layer structures. ft is not possible at present to assign definite geometrical positions to H2O in these layers. Nor can an explanation be given for the 571 JOURNAL MINERALOGICAL SOCIETY OF AMERICA

- BH,O-

N $ Or o. \,

oug,re .st,At Qo' Oon'

principal glide Frc. 2. Unit cell of vermiculite. The plane oi the paper is the parallel the b plane containing the origin of space group C%r,' The -y coordinates a*is are given in degrees. The origin is also a center of symmetry' 572 THE AMERICAN MINERALOGIST grad.ualdehydration as the temperature is raised. About 4 per cent of the HrO held as OH in the mica units should, however, be stable even at low red heat.

fxrpnpno:rarroN or. X_ney Dera ol Hyonoerorrrp 573 JOTIRNALMINERALOGICAL SOCIET:Y OF AMERICA given under chemical data, or in another combination, M-V-M- V_V_M_V-M-V-V- could It is not proposed that mica altering to hydrated material do so only in ratios 1M: 1V or 2M: 3 V, beforeit altered to vermic- Vnr.- TlsrE VIII' Pomrn DIAGRAMSo. MruBnlr-sFonuenr-v DssrcNeroo as Mrcur.rrEsAlrpt Hr.trrmc 24 Houts er 750"C'

12. Indices No"

1 9.40 9.56 3 v, Jo 3 002or 005 4.46 4.53 IL 4.50 t1,

J 4 1B 5 3 174 ti s.239 3 006or 0015 6 3.003 tx 7 2.861 2.861 0 2.880 Ip 2.873 rp 8 2.596 z 2.596 2b 2.613 4 2.601 3 9 2.424 z 2 413 It) 2.+3r 3b 2.423 2b 10 2.256 0.5 11 2 155 I 2.154 lb 2.r71 2.16r t2 2.06r 05 l.t 1.9710.5 |.977 i.b. t4 1.881 1.903 0.5 1.882 15 0. 1.8370 l6 t.674 tb lo 1.663 2b t.679 tt 1.628 I7.D 1.648 18 1.522 3 1.522 3 1.532 .5 1.524 t9 1.507 I 1..514I 1.506 20 1.453 0.5 1.461 0.5 1 L\'.) 2l l..tJr ID 1.350 1 | 363 tb 1.3.53 22 1.313 0.5 t.3r7 0.5 I. JZJ 2 1.315 23 1.293 0.5 r.296 1 1.290

ar: definite rnica reflection' 574 THE AMERICAN MINERALOGIST

for recording in the film, or that no definite unit cells, as far as the stacking of the layers is concerned, exist. No name has been suggestedfor such an heterogeneousarrangement of layers in one direction. The word metacrystalliaeis proposed to signify a state of partial change from one definite crystal structure to another without, however, attaining a homogeneousspace group arrange_ ment in one of the directions.

CoNcrusrows

An r-ray study of analyzed vermiculite minerals reveals the following facts: vermiculite exists as a distinct mineral. rts structural formula is (OH)r(Mg, Fe)3(Si,Al, Fe)aO16.4HzO.Its formula basedon the average of seven true vermiculites is 22MgO.5Al2Or. F2Os. 22SiO2. 40H2O. Ferr which is oxidized in the change from mica to vermiculite probably continues to occupy its Mg positions in the structure. The loss of K+ ions in this change is probably partly neutralized by the change of Ferr to Ferrr. The unit cell of vermiculite is monoclinic holohedral with the probable spacegroup C621,.as:s.3+A, bo:9.21 A. cs varies be_ tween 28.57 and 28.77 A in seven samples.g:97"09, I10,. The cell contains 4 molecules of the structural formula above. rts theoretical density is 2 13*. The structure consistsof (oH)aMg6(si,Ar)8o2r sheets, rike mica and talc, between which are interstratified layers of gHzO which occupy a space of definite thickness close to 4.9A. Compared with the structure of the chlorites these gH2O occupy almost ex_ actly as much space as the brucite layer 6Mg(OH), in chlorite. Though almost half of the HzO may be driven off at 110oC. no essential changes occur in the powder diagrams of specimens treatedin this manner. on heating vermiculite to 750' c. a collapseto the talc structure occurs. The well known exfoliation on heating seemsto be a simple mechanical disintegration of larger particles due to the formati,on of steam. The old term hydrobiotite is used again to designateinterstrati_ fication of "molecular" layers of biotite with vermiculite resulting in a new r-ray pattern. The word meta-crystalline is pro_ posed for such an arrangement and signifies a perfectly normal JOURNAL MINERALOGICALSOCIETY OF AMERICA 575 space group arrangement in all but one direction' In the latter the s"que.rce of layers or of units is heterogeneousto a certain extent. It may, however, as in specimens 9 and 10 approach a definite ratio of 1 : 1 : biotite units: vermiculite units' X-ray diagrams are necessary to distinguish vermiculite from hydrobiotite.

SUSSEXITE FROM IRON COUNTY, MICHIGAN CnBsrnn B. SrawsoN, [Jniaersity oJ Michi'gan' In 1930 seamanite, a new manganese phosphoborate was re- ported from the Chicagon Mine in Iron County, Michigan't Associated with the seamanite, but occurring in thin veinlets from 1mm. to 3mm. wide, was a white to yellowish-buff colored mineral which upon subsequent examination was shown to be sussexite. The sussexite occurs in the veinlets as irregular matted masses of fibers with the fibers lying parallel to the plane of the vein' These veins run through both the red "soft ore" hematite and the highly altered and porous cherty gangue' The gangue separates .uiily fro- the veins leaving thin sheets of the felted fibers of sussexite. small cavities or vugs within the veins are lined with yellow, transparent crystals of seamanite and in many instances they are implanted directly upon the sussexite.All the specimens in our possessionwere collected for the seamanite although the sussexiteis by far the more prevalent mineral. Sussexitehas a hardness of 3* and a specific gravity of 3'0 to 3.1. It is slowly soluble in cold concentrated mineral acids and in hot dilute acids. The elongation is negative, extinction parallel, and the indices of refraction for sodium light are: a:l'642, F: 1.713,and t:1.72I (all +0.003). The fibers are flattened so that most of them yield a and'p. Those resting on an edge give "y and exhibit a pronounced color dispersion which is greater than that of the methylene iodide mixtures usedfor the index determinations. The analysis given in Table 1 was made upon selectedmaterial which was crushed and washed with cold dilute hydrochloric acid to remove small acicular crystals of seamanite and microscopic cube-like rhombohedrons of calcite. Boron was determined by titration in the presence of mannitol, and the other oxides by ordinary gravimetric methods. HrO+110' was determined by the direct method recommended by Penfield using separate samples of approximately one gram each. It is interesting to point out that