MINERALOGICAL NOTES

THE AMERICAN MINERALOGIST, VOL. 51, MARCH_APRIL' 1966

NEW DATA ON ROEBLINGITE1

FnaxrrrN F. Forr, !n., Department of Geology and Mineralogy, The IJniaersity of Michigan, Ann Arbor, Michigan-

INrnorucrroN The roeblingite has been reported from two Iocalities: Franklin was Furnace,,and Langban, Sweden.The Franklin material frrst describedby Penfield and Foote (1897) as dense,white, compact massesof minute prismatic crystals associatedwith axinite, , datolite, barite, arsenopyrite,, titanite, and rhodo- chrosite,in or near the limestone-granitecontact. During an extensive mineralogical investigation of the Langban mineralsinitiated in the late 1920'sby G. Aminoff of the Natural History Museum, Stockholm, Sweden, a mineral similar in composition to roeblingite was discovered. A complete investigation of this new dis- covery demanded more reliable chemical data than was offered by Penfieldand Foote.Therefore, R. Blix (1931)performed several chemical analyseson the Franklin roeblingite in an effort to remedy the difficulty encounteredby Penfield and Foote in assigninga chemical formula. The chemical analyses from both sources are tabulated in Table I. Strunz (1957) reports the Langban roeblingite as possibly being orthorhombic with o:8.3, b:13.1, and c:12'65 A. Ho*evet' some difficulty is en- countered in obtaining a reasonable formula from the application of theseparameters to the available chemical analyses.

X-nav ANar-vsrs A specimenfrom each of the localities was investigated by both powder diffraction and single crystal methods. This investigation confirmed that roeblingite found at Langban is structurally identical to the Franklin material. A list of indexed d-values for roeblingite is presented in Table II. The space group as determined from precession and weissenberg photographs is cc or c2f c, corresponding to the diffraction symmetry 2/mC- /c. The unit cell has the parameters @: 13.27+0'03, 6:8'38 +0.02, c:13.09*0.03 A, and B:103.86+0'1o' Theseare the resultsof measurements made from Weissenberg and precessionphotographs of

1 Contribution No. 276 from the Mineralogical Laboratory, The Department of Geology and Mineralogy, The University of Michigan, Ann Arbor, Michigan' MINE,KALOGICAL NOTES 505

material from both localities. The parameters obtained for roeblingite from each locality were identical within the error of measurement.The parametersof Strunz (o:8.3, b:13.t, and c: 12.65A) apparentlyreflect the inaccuracy produced by assumingorthogonal geometry. The lattice shows a pseudo-mirror plane approximately perpendicular to the o-axis. consequently, an F-centered cell, closely related in dimen- sionsto the C-centeredcell, can be chosenwith o:13.27+0.03, b:g.3g

Tnsrn f. Crnurc,q.rAxar,vsns lxo Crrr Cor.rrnNrsol Rorlr,rNcrrr r.nou FneNrlrN Funx,tcr, Nnw Jrnsrv CellVolume:1,48 As

Penfield & Foote (1897) Blix (1931)

Oxide i^.:-... I Oxygen , Oxygen Latrons/ Latrons/ wt.7o Atoms/ Wt.Eo Atoms/ celI cell cell cel_t

Sioz 23.58 11.47 22.94 11.47 22.94 CaO 25.95 13.52 13.52 23.12 12.04 12.04 SrO l.4O 0.39 0.39 2.79 o.79 0.79 MnO 2.48 1.02 t.02 2.49 1.03 1.03 Na:o o.4o 0.36 0.18 KrO 0.13 0.08 0.04 HgO 6.35 20.62 10.31 6.15(+105" C.) 18.96 9.98 0.45(-105.C.) Pbo 31.03 4.06 4.06 30.04 3.93 3.93 SOe 9.00 ':' 10 81(SOt 3.95 11.85 COz T' 0.61 0.41 0.82

100.32 60.68 100.03 63.38

s.G.:3 .433

+0.02, c:2X13.13+0.03 A, andg: 104.56+0.1o.The choiceof axesfor the C-centeredcell definesthe perfect cleavageas {001} and the imper- fect cleavageas { 100}.

Crmlrrsrny X-ray fluorescenceanalyses were performed on samples of both Lang- ban and Franklin roeblingite. The results indicated that the sampleswere chemically similar and contained all of the major elements risted in the analyses(Table I). The number of cations and oxygen atoms per unit cell calculated from the analysesof Penfield and Foote (1897) and Blix (1931) is Iisted in 506 MINERALOGICAL NOTES

Tesr-B II. X-rav Pomrn Drllnacrrox Dete or Ronsr,rwcrrn lnoM LaNcnlx, Sweonx exn Fn.q'N

Relative d"r"(A) rndices d"r,.(A) d",r"(A) ._ lnolces d.r"(A) *::1:11; tntenslry

72 6 996 20 011 2.44 2.432 40 015

64 6.411 50 200 238 2.389 60 324 2.379 513 62 6.332 40 lo2 2.20 2.205 424 602 )l 5 187 30 202 2 200 2 .198 415 4 190 40 o20 2 1.94 520

4 063 30 202 211 2.|8 70 006 2 1tO 306 40 3 984 20 120 2 ro5 23i

3.9 3 896 20 311 209 2 .09.5 30 040

3.8 3.780 5 013 2.06 2 067 40 140 2 066 613 3.6 3.615 10 !94 1 944 142 3.5 3 462 10 311 1.942 1 934 3 434 40 113 1 930 726

3 198 70 102 1 910 40 620 3 196 313 1 909 IJJ 1 900 602 23-5 .JI 3 t66 80 204 1 897

30 2 999 90 320 1.84 1 846 2 993 213 I 841 7|, 1 840 700 294 2 926 r00 104 1.81 1.817 30 624 292 2 9t7 50 222 1 816 117 1 815 126 2.88 2 909 70 304 1 815 t.15 2 906 322 1.814 1.807 426 2.71 2 728 5 031 1.797 1 801 504 268 2 697 5 131 | 794 5tj r.789 704 2.53 70 422 2.53r 024 1.640 1.645 724 2.528 atl 1.641 151 2.526 224 1 638 442 1 636 208 2.496 115 MINERAI,OGICALNOTES 507

Table L The density used in these calculations was that of Penfield and Foote (1897).The spacegroups Cc and C2fchave equipointsof ranks 4 and 8. Both analyses, although yielding different numbers of oxygen atoms per unit cell, satisfy the requirements of the equipoint ranks. How- ever, the data of Penfield and Foote are more complete and conform more closely to the cation requirements of the equipoint ranks than do the data of Blix and are therefore preferred. Blix claims to have analysed for the alkali metals but fails to report their percentages.This omission accounts for much of the non-conformity of his analysis. In an effort to determine the structural role of the hydrogen atoms, a sample of roeblingite was analysed for loss of volatiles in a Bendix Time of Flight mass spectrometer. In this instrument, samplesare heated at a uniform rate (6o C./min.) while being subjected to an ultra-high vacuum (Pnro:5X10-u mm Hg). Volatile reaction products are ionized, sepa- rated into groups of ions of the same mass by a fixed potential, and dis- played by the instrument in the form of a "spectrum" of atomic masses. Thus, the operator is provided with the temperature of the reaction, the characteristics of the reaction, and the composition of the volatilized products. The loss of water vapor from roeblingite began at 40o C. and continued to 300oC., in what appearedto be one continuousreaction. This indi- cates that all of the hydrogen ions may be of the same type. However, the temperature at which roeblingite begins to lose water is characteristic of the lossof water from both with water of hydration and minerals with loosely bound hydroxyl ions. Consequently, only a tentative formu- la, (PbaSEOro)RroSiuOanHro,where R: Ca, Mn, Sr, Na, and K, basedon the analysisof Penfieldand Foote (1897),can be assignedto roeblingite. The determinationof the role of the hydrogenions must await structure analysis.

AcrlrowrplcEMENTS The writer is indebted to Dr. Donald R. Peacorfor his helpful advice during the courseof this study and for partial support under National ScienceFoundation Grant (NSF-GP-1790). The writer also wishes to thank Dr. JosephMandarino of the Royal Ontario Museum for furnish- ing a sample of Franklin roeblingite and Dr. Frans Wickman and O. Gabrielsonof the SwedishMuseum of Naturai History for their verifica- tion of the Langban sample (University of Michigan Museum) as being roeblingite and for their generousinformation concerningthis mineral. lastly, the writer wishes to thank the Bendix Systems Division of Ann Arbor, Michigan, for the use of their Time of Flight mass spec- trometer. 508 MINERALOGICAL NOTES

RnlBreNcns

Br.rx, RacNan (1931) The chemical composition of roeblingite. Am. Mineral' 16' 455-460. Dorr-rnn, C. (1914) Hand,buch Der Mineralchemie,Band II. Verlag von Theodor Stein- kopff, Dresden und Leipzig, 805-806. FIrNrzr, C.qnr. (1938) Hand.buch Der M,ineralogie, Ergtinzungband, I, Neue Mineralien. Walter De Gruyter and Co., Berlin und Leipzig,569-57O. - (1960) Hantlbuch Der Mineralogi,e, Ergtinzungsband II, Neue M'ineraJnamen. Walter De Gruyter and Co., Berlin,469. LmsEn, Esper (1921) The microscopic determination of non-opaque minerals. u.s. Geol. Staoey Bul'l'. 679, 127. PAI-ecnn, crrerr-ns (1928) The phosphorescence and of Franklin Minerals. Am. Mineratr. 13. 330-333. Prxurr-o, S. L. eNo H. W. Foorr (1897) Ueber Rttblingit, ein neues, schweflige saure und Blei enthaltendesSilicat von Franklin Furnac e,N .J- Zeit. Krisl. 28' 578-580' Srnumz, Huco (1957) Minerologische Tabellen. Akademische Verlagsgesellschaft, Geest & Portig K. G., Leipzig, 272. wrNcnErr,, N. H. eND A. N. WrNcnntr (1927) El,ements of optical Mineral,ogy, Port II, Descripti.onsof Minerols. John Wiley & Sons, Inc., New York, 406'

THE AMERICAN MINERALOGIST, VOL. 51, MARCH_APRIL, 1966

HOLLOW CHRYSOTILEFIBERS

R. A. Cr,rnroN,JR., C. W. HuccrNS ANDH. R. Snnrr', Norris Metallurgy ResearchLaboratory, Bureau of Mines, ' U. S. Department oJ the Interior, l{orris, Tenn'

INrnorucrroN The ,,hollow tube,' theory for chrysotile was establishedwhen Turke- vich and Hiller (1949) published electron micrographs indicating that singlefibers were hollow tubes.This theory was further substantiatedby the work of NolI et aI. (1958), Huggins (1962), Zussman and Brindley (1957), Bates et at. (1950), Maser et al' (1960), and others. Conversely, Pundsack (1956, 1961), and Kalousek and Muttart (1957), concluded that the density of chrysotile blocks was incompatible with either tubular or solid cylinders. More recently, Whittaker (1963) and Bates (1958) have hypothesized that chrysotile fibers are filled with amorphous or partially oriented material and that this accountsfor the lack of voids in the fibers.The recentpublication by Huggins and Shell (1965)on density of bulk chrysotile and massive serpentine shows that the density of Arizona and African chrysotile is compatible with tubular structure, and that Canadianchrysotile, which has a higher density, has at least 50 per cent unfilled tubes.