NORSETHITE, Bamg(Cog)2, a NEW MINERAL from the GREEN Rr

THE AMERICAN MINERALOGIST, VOL 46, NIARCH APRIL, 1961

NORSETHITE, BaMg(COg)2,A NEW MINERAL FROM THE GREEN Rr\rER FORI,IATrON, WYOMTNG*

M,q.nvE. Mnosn, E. C. T. Cneo, Josuru J. Fanov, ANDCHARLES MtttoN, U. S. GeologicalSurvey, Washington 25, D. C.

Assrn,{cr

Norsethite, BaMg(CO):, was found in dolomitic black oil shale below the main tiona bed in the Westvaco trona mine in Wyoming, associated with shortite, labuntsovite, searlesite, loughlinite, pyrite, and quartz. It also occurs there in gray shale with abundant shortite and northupite, some searlesite and loughlinite, in a fine-grained matrix consisting essentially of quartz and pyrite. Norsethite occurs as clear to milky-white circular plates or flattened rhombohedral crystals, 0.2-2.0 mm. across. The mineral is insoluble in water but is readily decomposed by cold dilute hydrochloric acid. Norsethite has hardness about 3.5; density 3.837+0.005 (meas.),3.840 (calc.); luster vitreous to pearly; fracture hackly; good rhombohedral cleavage. It is infusible before the blowpipe. Norsethite is uniaxial negative, and the indices of refraction are a:1.694 and e:1.519. X-ray crystallographic studies show that the crystals are rhombohedral and have the following characteristics: possible space groups, RBzz, R3m, or R32, the most probable being R32 (D37),a subgroup of R3c, the space group of cal- citel hexagonal a-5.020+0.005 A, c:16.75t0.02; rhombohedral a6,:6.29'10.01 A, a:47"02'*05t1 volume 365.6 A3 (hex.);cell contents: 3[BaMg(CO)z], in the hexagonal unit. Crystalforms observedarec{10001}, a lll20l,m {10T0},and r {1011}.Thestrongest r-ray lines are:3.015 A (too),3.860 (35), 2.656 (35), 2.512 (35),2.104 (35), 1.931 (35), 1.864(35). Norsethite has a structure similar to that of calcite. The structural relations of norsethite. dolomite. and calcite are discussed. Chemical analysis of a 0.1 gm. sample gave: BaO 52.9,CaO 0.5, MgO 13.9, FeO0.4, MnO 0.1, COz3l.2, Na2O 0.2, SiOr 0.3, insoluble 0.4, total 99.9 per cent. Norsethite is named in honor of Mr. Keith Norseth, engineering geologist of the trona mine at Westvaco, Sweetwater County, Wyoming.

INrnonucrroN The new mineral norsethite,BaMg(COa)2, was discoveredduring the investigation of the authigenic minerals of the Green River formation of Wyoming, Utah, and Colorado. ft occurs in microscopic quantities at the Westvaco trona mine which is about 18 miles west of Green River, Wyoming. So far, norsethite has not been found at any other Green River locality. The specimensthat containedthe crystalsof norsethitewere collected by Charles Milton who first observed this new mineral and named it in honor of Mr. Keith Norseth, engineeringgeologist at the Westvaco trona mine, in grateful acknowledgment of his friendly assistancein the mineralogical studies of these authigenic minerals.

Publication authorized by the Director, U. S. Geological Survey. 420 NORSETHITE,BaMs(CO)z 42r

OccunnpNcB ol NoRSETHTTE Norsethite first was observed as clear to milky-white plates flattened parallel to the basal pinacoid (Figs. 1 and 4) in the dolomitic black oil shale which underlies the main trona bed at the Westvaco trona mine in Wyoming. There the mineral has been found associated with shortite [NazCaz(COt r], labuntsovite [(Na,K) z(Ba,Mg) (Ti,Al, l'e,Nb) zSiaOrr (OH)ul, searlesite[NaBSizOo' HrO], loughlinite [NazMgeSioOre'8HzOl, pvrite, and quartz. Norsethite also occurs at the Westvaco mine in a gray shale that consists largely oI quartz and a small amount of pyrite; the associated minerals are abundant shortite and northupite [NaaMgCI(CO3)2],and lesseramounts of searlesiteand loughlinite. The water-insoluble residue of trona core from an unknown depth, drilled in the area of the Westvaco trona mine, yielded discoid masses of norsethite(Fig. 2).In addition, good crystaisof the type shownin Figs. 1 and 3 were obtained from the waste ssdiurn carbonate "mud" dis- chargedfrom the soda-ashprocessing plant at Westvaco,along with pyrite, shortite,dolomite, calcite, labuntsovite, barytocalcite ICaBa(COr)z], leucosphenite[Na3CaBaBTisSisOzs], and witherite [BaCOs]. Thus far, norsethitehas not been found in the dolomitic oil shalesof Utah or Colorado. MrNnnar, SrpenerroN Norsethite crystals were isolated from the rock specimens,the trona core, and the lvaste sodium-carbonate"mud" by heavy-liquid separation (bromolorm), followed by hand-pickingunder the binocular microscope. Associatedwith norsethitein the waste "mud" were crystals of barytocalcite and witherite, nearly identical in habit with those of norsethite. Norsethite could not be distinguished readily from barytocalcite and witherite by means of indices of refraction, or by specifrcgravity, since Clerici solution attacks carbonates.It was necessaryto check eachindi- vidual crystal of such habits under the microscope;norsethite is uniaxial negative,whereas barytocalcite and witherite are both biaxial negative with small 2V. The material submitted for the chemical analysis (0.1 gm.) was obtained from a single specimen of dolomitic shale which was free from barytocalcite and witherite. In this instance only bromoform separation was required.

Puvsrcar,lNl Oprrcrlr- PnopBnrrns Norsethite occurs as clear to milky-white circular plates or flattened rhombohedral crystals with diameters ranging from 0.2 to 2.0 mm. (Figs. 1-4). Some crystals, as well as irregular grains, show corrugated M. E. MROSE, ET AL,

d E

4i bo

>5 Oa'

6u E:il tr

'AatNi )

MO'

>>'l

a2l Q bar :or '9 l : ZE) *6id NORSETHITE,BaMg(COs)z 423 or flattened edges; the thick corrugated grains are pumpkin-shaped. The mineral has a vitreous luster, a hackly fracture, and good rhombohedral cleavage{1011}. Its hardnessis about 3.5. Norsethite is insoluble in water but is readily decomposedby cold dilute hydrochloric acid. It is infusible before the blowpipe. The specific gravity, determined on small crystals of norsethite on the Berman microbalance, using toluene as the immersion liquid, is 3.837+0.005 (an averageof six different de- terminations); for large crystals, 3.81010.005; the calculated specific gravity is 3.840. Most of the crystals of norsethite that were examined

Fro. 5. X-ray powder photographs (Cu Ka radiation). (above) Calcite, Westvaco trona mine, Sweetwater County, Wyoming. (middle) Norsethite, Westvaco trona mine. (beiow) Dolomite. Binnental. Switzerland. under the microscopeshowed fluid inclusions or cavities; some appear as channelsnormal to, and in between,the rhombohedralfaces, as shownin Fig. 1 and 4. The presenceof cavities and channelsin the large crystals undoubtedly accountsfor the differencebetween the observedand calculated values. Optically, norsethite is uniaxial negative. The mineral is colorlessin transmitted light. The indices of refraction were determinedby the immersion method using sodium light and were corrected to 25o C. The error of measurementprobably is not greater than *0.001; a:I.694 and €:1.519;A:0.175 (Na). The rule of Gladstone and Dale l(n-I)/d:Kl was found to hold surprisingly well for norsethite. Norsethite with d:3.837 (meas.) and K:0.16632 (based on the recalculatedchemical analysis in Table 3) givesdKf 1:1.638 for the calculatedmean index and (2a-le)/3:I.636 for the measuredmean index. 424 M. E. MROSE, ET AL.

CnvsrenoGRAPHY Morphology The faceson the well-formedcrystals of norsethitegave only fair sig- nals on the opticai goniometer. The forms observed were identified readilyfrom goniometricmeasurements correlated with the single-crystal o-ray results. The morphology of the largest crystals measured (averag- ing 1.0 mm. in diameter) consistsonly of a well-developedbase [00011 and the rhombohedron{101 1}. The small crystals (lessthan 0.5 mm. in diameter) showed, in addition, the first order prism {1010} and the secondorder prism [tl20l, as very narrow faces. The notable absenceof a bipyramidal form on any of the numerous crystals examined made it impossible to determine the crystal classfrom morphological considerationsalone. The crystals are holohedral in habit. They gave no positive piezoelectricresponse on the Giebe-Scheibeappa- ratus. This evidence would suggestthat the crystal classis either rhombohedral(3) or scalenohedral(32/m). Both thesepossibilities were elimi- nated and the crystal classwas establishedas trigonal-trupezohedral (32) from a consideration of the space group criteria and the structural relation of norsethiteto calcite (seediscussion on page 426). X-ray powd.erd.ata An r-ray powder diffraction pattern of norsethite(film no. 11793)was taken in a 114.59mm. diameter Debye-Scherrercamera with nickel- filtered copper radiation (X:1.5418 A), using both the Straumanisand Wilson techniques(Fig. 5). Film measurementswere corrected for shrinkage. AII interplanar spacingsand intensitiesfor the observedlines are given in Table 1, column 2. The intensitieswere estimated visually by comparisonwith a calibrated intensity strip. Interplanar spacingswere calculatedfrom the s-ray cell constants down to a value of d6.,:1.995 A otr a digital computer using a program developed'andcarried out by Daniel E. Appleman. All calculatedspacings lor d'ntr) 1.000A for norsethite are listed in Table 1, column 1. Single-crystalx-ray d.ata A thin, tabular, hexagonal-shapedcrystal of norsethite (approxi- mately 0.5 mm. in diameter) was examined by the Buerger precession method. A. quartz-calibrated precession camera was used with zir- conium-filtered molybdenum radiation (I:0.7107 A) to obtain the h0.1,hI.l,, hk.O, hk.l, and hh'I net planes.These photographsestab- lished the lattice as rhombohedraland, together with the film measure- ments (correctedfor horizontal and vertical shrinkage),Ied to the crys- tallographicdata given in Table 2. NORSETHITE, BaMg(CO)z 425

Tasr,r 1. Coupenrsowor X-Rev porlorn Dar,r ron Nonsrrnrrn. Dorourrr, ANo Car,crre

Dolomite,CaMg(C( Calcite, CaCO3 RossTownship, q.,- +1"^r:^ Haley, Ontario Swanson and Fuyat, Flowie and 1953 Broadhurst, 1958

(1) (2) (3) (4) Calculated. Measuredb Measured" Measuredd

hk.l dn+t dn* t 00.3 5 583 5.584 25 10.1 4.208 4.210 30 4 025 J ot.2 3 .859 3 .860 35 3.690 3.86 12 10.4 3 016 3.015 100 2.886 100 3.035 100 00.6 2.792 2.795 2.670 10 2.845 3 01.5 2 654 2.656 35 2.540 8 11.0 2.510 2.512 35 2.405 10 2.495 t4 tt -J 2.289 2 290 25 2.192 30 2.285 18 02.1 z.lJo 2 154 25 2.066 15 20.2 2.104\ 2.015 I5 2.095 18 r0.7 2.0e61 2.104 35 02.4 | 929 35 r.927 5 01 .8 1.886 25 20 1.913 ll lt o 1.8671 1.875 1i 00.9 | .86rl 1.864 .t.) 30 20.5 1.824 1.824 2t.l I O.t.) r oJo 6 1.567 r.ozo 12.2 I 612\ r.612 18 02.7 1.60e I 10 10 1.563 1.563 6 1 496 2 1.587 2 21.4 1.530 1..530 25 1.465 5 1.525 q 20.8 1.508 I .510 o | 445 4 1.518 n 11.9 1.495 | 496 o | 431 10 1.510 J 12.5 r.475 1.475 9 1.413 4 |.473 2 03.0 1.449 7.448 o 1.389 -tJ r.M0 01 11 l.+Jl | 437 z 03.3\ s03J 1.404 6 00.12 1.396 1.398 6 8 I All 1 355 I JJO 9 A I .356 02.10 1 327 1.328 9 1.339 128 1.293 1.295 o | 297 03.61 so.61 1.286 1.286 9 22.0 1 255 1 256 o |.247 20.11 1.247 1 248 4 10.13 1.235 1.237 .) 223 1.224\ 1.235 11.12 1.2201 | 222 9

13.I r.203 J

(Continued, on nert page) 426 M. E. MROSD, ET AL.

Tarr,r 1 (Continued.)

rite,CaM Norsethite, BaN{g(COg)z Calcite, CaCO3 Ross Ton'nship, Westvaco trona mine, Synthetic Haley, Ontario Co., Wyoming Swanson and Fuyat, Sweetwater Horvie and Present Study 1953 Broadhurst, 1958

(1) (2) (3) (4) Calculated' Measuredb Measured" Vleasuredd

hk.t dn* t dt* t dnnt 31.2 1.193 r.193 4 1.144 21.10 1.173 r.173 A 1 123 1 1795 13.4 1.159 1.160 9 1 1538 01.4 1.154 I . _tJ+ 3 22.6 1.145) 03.9 1.1441 1.144 A 1.096 30.9 1.1M) 31.5 1. 135 o 1 068 00.ls] r'rr/1 1" ,t 12.11) 02.13 1.108 1.108 3 40.1 1.084 1.086 3 04.2 1.078\ 1.077 o t3.7 1.077I 40.4 1.052 1 051 r.0473 J 20.14 1.048 1.046 o 1.0613 1 1.042\ 1.0447 31.8 J 22.9 | .041I 04.5 1.034 3 11.15 1 020 A J 1.0352 10.16 1.018\ 3 0.973s 2r.13 |.Or4J r.0234 <1 03.12\ r nn( 1.006 6 0.962 5 1.01 18 2 30.121 0.9893 3 0.949 I 0 989s <1 o 9799 3 0 930 1 0.9846 1 0 9717 6 o.926 3 o 9782 I 0 9683 6 0.923 3 v.9lol 3 0.9559 3 0 913 1 0.s655 2 0 9499 3 0.909 2 0 9469 3 0 903 1 0 9343 4 0 894 2 0.9223 3 0.835 n 0 9117 3 0 821 2 0.9017 4 0 8989 6 0.8961 3

* This line was obscured by a Iine of the Si standard' Structural relation to calci'teand. dolomite A search oI crystal Data (Donnay and Nowacki, 1954) showed that dolomite ICaMg(CO3)2]and calcite ICaCOa]have cf a ratios remarkably close to that of norsethite [BaMg(cos)2]. This, coupled with the fact that these three minerals have remarkably similar crystallographic data (Table 2) as well as physical and optical properties'strongly suggested NORSETHITE,BaMg(COa)z 427

that norsethite must be a member of the same structure group as dolomite and calcite. Comparisonof the r-ray powder films (Fig. 5) and the powder diffraction data (Table 1) for the three minerals indicated a strong structural resemblancebetween norsethite and calcite (space group R3c), and betweennorsethite and dolomite (spacegroup R3). The Buergerprecession photographs of norsethiteindicated only three possiblespace groups for the mineral: R3rn, R3m, or R32. Neither R3aa nor R3rn is a possiblesub-group of R3c or of R3. Since evidenceindicates that norsethitehas a structure similar to that of calcite, and sinceR32 is the only one of the three possiblespace groups for norsethite which is listed as a sub-groupof R3c (the spacegroup of calcite),it follows that the spacegroup of norsethitemust be R32. In order to elucidate the relation of the norsethite structure to the calcite and dolomite structures, a determination of the structure of norsethite has been undertaken and will be published in detail at a later date.

T,qnr,n 2. CoulanrsoN or Cnysrer,rocn.a.pnrc Dar.q. lon Nonsrrnrro, Dor,ourrr, luo Cer,crre

Mineral Norsethite Dolomite Calcite

Locality Westvaco mine, Sweet- Ross Township, Ha- Synthetic water Co., Wyoming ley, Ontario

Present Study Howie and Broad- Swanson and Fuvat, hurst, 1958 1953

Symmetry Hexagonal-R; trapezo- Hexagonal-R; rhom- Hexagonal-R; scale- hedral-32 bohedral-3 nohedral-32/m

Cell Constants a 5.020 + 0.005 A 4.810+0.002A 4.9S9A c 16.75+0.02 1602 +0.001 r7.062 c/a J.JJ/ 3.330 3.420 &rlt 6.29+0.01 A 6.020A 6.37sA q 47"02',+05', 47"07', 46"M'

Space Group

Volume (hex.) 365.6 A3 321.0 A3 367.8A3 Cell Contents (hex.) 3[BaMe(CO3)r] 3[CaMg(CO)i] 6[CaCOe] Density (calc.) 3 .840 2.872* 2.7rr (obs.) 3.837+0.005 2.86*

* Quotedfrom Zen (1956). 428 M. E. MROSE,ET AL.

CuBlrrsrnv Except for the determination of COz, the classical procedures of Hillebrand et,al. (1953)were followed in the chemicalanalysis of norsethite which was made on a 0.1 gm. sample obtained from a single specimen. Carbon dioxide was determined volumetrically by measuringthe gas evolved when the sample was treated with (1*3)HCI and, after reducing to standard conditions, appiying the factor to convert volume of COz to mass (Fahey, 1946). The quantitative spectrographic analysis for minor elements in norsethite,cited below, was made by Harry Bastron of the U. S. Geo- logical Survey: Ca 040 Sn 0.002 Na 0.2 Ti 0.001 Fe 015 Cu 0.0005 Mn 0.049 Cr 0.0004 Sr 0.022 Be 0.0002 Al 0.016

Looked for, not found: Ag, Au, Hg, Ru, Rh, Pd, Ir, Pt, Mo, W, Re, Ge, Pb, As, Sb, Bi, Te, Zn, Cd, Tl, In, Co, Ni, V, Ga, Sc, Y, Yb, La, Zr, Th, Nb, Ta, U, Li, P, and B. The chemical analysisof norsethiteis given in Table 3. The formula derived from this analysis is BaMg(COs)2. The recalculatedchemical analysisis in good agreementwith the theoretical composition.

T,r.sLE3. Cnnurc,rr-ANer-vsrs or Nonsrrnrre, BaMg(CO)z Analyst:J. J. Fahey

Determined Recalculated Per Cent

BaO 52.9 53.5 CaO 0.5 0.5 Mso 13.9 74.O FeO' 0.4 0.4 MnO 0.1 0.1 COz 3r.2 31.5 Nuron 0.2 SiOr" 0.3 Insol d 0.4

u Total iron as FeO. b Determined spectrographically by Harry Bastron. " Soluble in (1*3)HCl. d Insoluble in (1t3)HCl. NORSETII ITE, BoM g(COs)z 429

Using the measuredspecific gravity determinationof 3.837,the chemical analysisin Table 3, and the cell constantsfor norsethite,the experi- mental molecular weight of the unit cell is 844.6. The calculated cell contents approachvery closelythe formula 3[BaMg(CO3)r].

AcxNowr,BocMENTs We are grateful to thesecolleagues in the U. S. GeologicalSurvey for their assistance:Howard T. Evans, Jr., who contributed helpful advice and discussion;Daniel E. Appleman, rvho calculatedthe d-spacingson a digital computer; Harry Bastron, who made the spectrographic analysis;and Isidore Adler, who checkedthe crystals of norsethite for piezoelectricity. Rnrenrxcrs

DoNNev, J. D.H. .Luo Nowacrr, WnnNl;n (1954), Crystal Data GeoLSoc. Arnerica Mem- oir 6O. Fauov, J. I. 0946), A volumetric method for the determination of carbon dioxide zz Wells, R.C andothers,Contributionstogeochemistry,194245;Lr.S.Geol.Surtey&utrtr.95O, t39-141. Hrr,r,ennem, W F., Luuorr,l, G. E. F., Bnronr, H. A., eNo Hor.lue.N, J. I. (1953), Ap- plied inorganic analysis, 2nd ed. John Wiley and Sons, Inc., New York. Howm, R. A. nNt Bnoannunsr, F. M. (1958), X-ray data for dolomite and ankerite: ,4a2. M,inerol., 43 1210-1213. " INrnnNarrowar,n T,llrr,r,rN zun BnsrruuuNc voN Knrsl.q.r,r,srnuxrunnN (1935), 1, p. 264. Gebriider Borntraeger, Berlin. Swa.NsoN,H. E. e,r'nFuvar, Rurn K. (1953), Standard X-ray diffraction powder patterns: U. S. Natl,.Bur. Stand.ard.sCirc. 539,2,51-54. Zru, E-AN (1956), Correlation of chemical composition and physical properties of dolomite: Am. Jour. Sci.254,51-60.

Manuscript receited lune 18, 1960.