American Mineralogist, Volume 65, pages II38-1142, 1980

Okanoganite, a new rare-earth borofluorosilicate from the Golden Hom batholitb OkanoganCounty, Washington

Russnrr C. Boccs Departmentof GeologicalSciences, University of Califurnia Santa Barbara, Califurnia 93106

Abstract

Okanoganite is found in miarolitic cavities in the arfvedsonite phase of the Golden Horn batholith, near Washington Pass,Okanogan County, $y'ashington.It occurs as tan to pale pink pseudotetrahedraltwinned crystalsup to 4 mm across.A combination of electron microprobe analysesand spectrophotometric analyses for B2O3give the following formula: (Nau*Car.*Pboro)[(Y,Ce,Nd,La)rr".rCar.^Fe,u,](Si,r rrTlo*)Bu*Or, -F42.4r,with an ideal for- mula of (Na,Ca)r(Y,Ce,Nd,La),rSi5B2O27FA.The crystals are pseudotetrahedralfourlings with twin plane {0114}, the c face of each individual forming the faces of the pseudo- tetrahedron. The is rhombohedral with possible spacegroup R3, R3, R32,R3m, R3m, R3c,or R3c.The cell dimensionsare 4 : 10.12(l),c : 27.05(8)A,Z:3 (hexagonalcell) or a :10.94(3)A,a:58.?(3)",2:l(rhombohedralcell).D(meas):4.35,D(calc):4.37.Ttie strongestlines [4 I), (hkl)l of the X-ray powder pauern (68 given) are 4.38(4\QA); 3.rr(a8)(300); 2.e70(100X027); 2.e3e(e5)(125); 2.e26(s0)(303); 2.676(32)(220); 1.978(35X325,413);1.822(32)(3.0.12); 1.784(43X330,2.0.14). The refractive indices are a : 1.753,e: 1.740;the mineral showsno dichroism and is colorlessin thin fragments; : white; H : 4. It showsno fluorescenceor phosphoresoenoeunder UY radiation and does not cathodeluminesce.The nane is for OkanoganCounty, $y'65hington.

Introduction Occurrence The Eocene Golden Hom batholith crops out over Okanoganite occurs in miarolitic cavities, which 310 km' in the northern CascadeMountains in range from I to 5 cm in diameter, within the per- Okanogan, Chelan, and Skagit Counties, \{65hing- alkaline arfvedsonite granite phase of the Golden ton (Stull, 1969). Horn batholith, which crops out as an approxinately Miarolitic cavities in the batholith contain a num- horizontal zone between 1800 and 240o m in eleva- ber of rare and unusual , including at least tion in the southeasternpart of the batholith. I first two new minerals, zektzeite, NaLZrSioO,, (Dunn el found the mineral as only a few small crystals (less al., 1977), and okanoganite, named for Okanogan than ten mg) in two cavities in September, 1976. County. The mineral and the name were approved Later additional material of better quality was found by the Commission on New Minerals and Mineral by Robert M. Boggs on specimenshe collected in Names, IMA, prior to publication; the name is pro- August, 1976,and the descriptionis basedchiefly on nouncedoh-ka-NOG-an-ite. Type material has been this material, which totals a few hundred milligrams. deposited in the mineral collection at the University Associated minerals within the cavities, which of California, Santa Barbara (specimens#UCSB show no zonation of the minerals, are , micro- 8256 and 8257).Cotype material has been deposited cline (perthite), zircon, arfvedsonite, bastnaesite,zek- in the National Museum of Natural History, Smith- tzeite, astrophyllite, a pale green mica (probably sonian Institution, Washington, D.C. (NMNH polylithionite, based on its optics and contents of #142512 to 142514),and in the collection of the au- SiO2,Al2Or, trlrO, and F, there being insufficient ma- thor (specimens#T550 to T555). terial to determine the LirO content), and an uniden- 0003-004x/80/lI 12-l 138$02.00 l 138 BOGGS: OKANOGANITE I 139 tified calcium rare-earthminsl4l goil4ining fluorine. s{l0la} bevelingthe edgesof the crystals(Fig. lc). A Other minerals found in the miarottic cavities, but few crystals show an interpenetrating lwinning with not associatedwith okanoganite, include acmite, the additional composition plane {1012} (Fig. ld). plagioclase, elpidite, gagarinite, allanite, prehnite, The twin law is the same in both cases,and is de- epidote, fluorite, titanite, siderite, biotite, monazite, scribed by a l80o rotation about a twin axis per- calcite, galena, anatase, fayalite, thorite, gadolinite, pendicularto {0114}. and several as yet unidentified minerals. The crystals have a hardness of 4. In a few cases The sequenceof formation in the miarolitic cav- the surface is altered to a softer material. In a few ities containing okanoganite was as follows: (earliest) specimensthe okanoganite has altered to an uniden- arfvedsonite, microcline, quartz, astrophyllite, Kk- tified calcium rare-earth mineral 666aining fluorine. lzerite, zircon, okanoganite, polylithionite, bastnaes- This mineral, which also occurs as light yellow- ite, and an unidentffied calcium rare-earth mineral brown tabular crystals of crude hexagonal outline (atest). and less than 0.5 mm wide, could be a carbonate of the parisite group. Physical properties, habit and twinning Okanoganitehas a densityof 4.35(+0.04) gm/ctr, Okanoganite crystals are tan to pale pink and are measuredwith a Berman balanceon a 21.3mg crys- generally about I rlm across,with the largest crystal tal cluster in toluene at 21"C. Using the observed ra- found being 4 mm across. They occur both as iso- tios of rare-earth elements and a Na:Ca ratio of lated fourlings perched on crystals of microcline, arf- 2.5: I gives a calculated densrty of 4.37 gmlcm', in vedsonite,zircon, andzektzeite and as compactly in- good agreement with the measuredvalue. Okanoga- tergrown clustersof crystalsup to 8 X 4 x 4 mm. nite is uniaxial negativewith ar: 1.753and e: 1.740 The crystals appear to be isometric tetrahedrons, (each +0.002) in white light, shows no dichroism, is but are actually fourlings twinned on composition colorless in thin fragments, and has a white streak. plane {0114} with the c face of eachindividual form- Okanoganite does not fluoresce or phosphoresoeun- ing the faces of the pseudotetrahedra(Figs. la and der either long or short wave UV radiation, and does lb). A few crystals have minor faces of the form not cathodeluminesce. Applyng the Gladstone-Dale relationship with the constantsof Mandarino (1976)gives a value of K. which ranges from 0.149 to 0.166, depending on which value of k for YrO, is used (0.170or 0.195) (Mandarino, 1978),whether the Fe is consideredas FeO or FerOr, and whether any or all of the Ce is CeOz. The measured refractive indices and density give a value of 0.172 for ^fii. This gives values of (l-K,/K) which range from 0.186 to 0.036. These values indicate poor to excellent compatibility be- tween the density, refractive indices, and chemical composition(Mandarino, 1979\. X-ray crystallography A tabular single crystal was prepared by cement- ing one of the twinned crystals to a glassslide on one of its c faces and grinding away most of the other three individuals. All the crystals have slightly curved faces, resulting in multi-domained crystals which produce poor quality single-crystal photo- graphs. The cell dimensions were determined from this crystal by means of an hlco precession photo- Fig. l ldealized drawings of crystals of okanoganite. The graph and an hol Weissenbergphotograph. The cell by the subscripted individuals in each fourling are diferentiated from a least-squaresrefinement of the X- numb€rs. Forms present are c{0001} and s{10f4}. Drawing b dimensions shovs a fourling with one of the individuals separated to better ray powder diffraction pattern (Table l) run on a dif- show the twinniry relationshiP. fractometer at a scan speed of lo /min, standardized I l,tO BOGGS: OKANOGANITE with annealed slmthetic CaF.. (a : 5.459A), using R3, R32, R3m, RIm, R3c, or Ric. A Laue photo- CuKa radiation(I : 1.54178A;are: a: 10.72(l),c : graph made as an attempt to further define the space 27.05(S)A (hexagonal cell) or a : 10.94Q)A, c : group was inconclusive due to its poor quality. 58.7(3)' (rhombohedralcell). The single-crystal photographs and the lines of the Chemical composition powder pattern with d values greater than 3.00A Two crystal clusters were embedded in epoxy, showed the extinction -htk*l:3n. and all lines of ground and polished, and coated with approximately the powder pattern could be indexed to observe this 200A of carbon. Analyses were made with an ARL extinction. It was not possible to confirm or deny any electron microprobe, using an acceleratingvoltage of other extinctions due to the poor quality of the pho- 15 kV and a sample current of l0 nanoamps.The tographs. This indicates as possible spacegroups: R3, spot size was 20 pm. Standards used were rare-earth,

Table L X-ray powder diffraction data for okanoganite and a related unnamed rare-earth fluorosilicate from Siberia

Siberian rare-earth Olrenoooni to Siberian f lmro-si11cate* Okanogmite rare-earth fluoro-silicate*

hkr, d _ d- I, q. I _ hkr d - d. r. I. calc obs oDs oDs obs calc obs obs oDs oDa

003 9.O2 9.0r 4 505 r.756 t.755 18 t.755 0r2 7.65 7.67 12 r.2.14 r.693 1.695 4 104 5,47 5.48 7 o57 r.673 I 110 5.36 5.35 7 iis i:;;; i t'672 16 r.674 20 015 4.67 4.67 13 lsq -'---I co2 \ | r. sgo 6 1.596 t5 021 4.57 4.57 5 0.2.16 1.s89J 202 4.39 4.3s 41 4.34 3.0.rs 1.558l 024 ,^^' :'-:- ) r.558 o 3.83 3.82 426 r.)) I l r07 3.57 3.57 20 339 1.535 1.535 LZ L. J'I 205 3.52 3.5r 18 517 r.531\ o.s.ro i:sai r'532 13 I22 3.39 3.39 16 J.Z5 20 i 2r4 3.1r 1 603 r.525 r.527 r' rL 48 3.10 50 .I0 3oo 3.09 I 4.1.12 1.507 r.s07 o 1.510 20 009 3.00 3.01 15 502 1.486 r.487 7, 1.486 20 027 2.970 2.970 100 ) 01 345 r.468 t.469 10 523 t.466 r.466 12 l. 4b) r25 2.943 2.939 9) 25 303 2.926 2.926 50 ?.93 80 2.3.L4 1.43I r.432 4 208 2.733 2.734 l5 2.73 15 4.2.tt t.428 | .428 220 2.679 2.676 32 50 526 1.411 \ 1.409 J I.+II r.0.10 2.597 2.598 20 2.60 20 6t2 r.408 l 131 2.562 2.564 9 35r 1.326) I ?tq 306 2,551 2.554 9 70r r.326 | 8 312 2.528 2.525 7 L.325 ) 134 2.405 2.404 4 532 1.321) 0.r. lt 2.377 2.371 4 072 1.32I l 1.318 l0 1.320 0.2. l0 2,337 2.338 4 2.r. L9 1.320 t 315 2,324 2.318 4 0.4.17 1.313 1.313 042 2.287 2.285 4 2.3.t7 I.275 r.274 9 1.280 z) 404 2.t95 2.t93 b t.2.20 t.262 1.262 4 ,)\ 309 2.156 2.t54 26 2.15 2.5.t2 1.242 I.241 L. Z4) 20 078 1.236 137 2.t42 2.14r to \ L.238 6 232 2.101 tl 538 t.236 ) .2.103'l 2.O9 324 2,031 4. J. IJ 1.23I\ 1 zaQ z'uru 24 2.03 J r.o. t3 z.ozo I 6.1.l1 t.228 ) 229 2.000 r.996 l9 oz I L.223\ r.221 'l 173 r.220 235 1. 981 'lI L't t6 35 r.972 50 0.3.2t 1.reo r43 t,slo I o.2. 13 1.899 L.891 4 1.905 541 r.189| 20 ittt 327 1.865 \ 1.r89 | 1.188 r' 600 L2 1.864 20 r.3. ro r. sos / 5. 1.16 r. r88 | r76 r.r87 ) 3.O.r2 t.822 r.822 32 1.828 60 0.0.15 r.8041 3.2.19 r. 184 1.r84 8 r'uuu 238 t,aot,l 7 L.179 l. r80 330 1.786I o.t.rc 1.143 1.143 9 L' to+ 4J 1.785 547 I.137 z.o.r4 lta+ J \ 1.135 7 805 L.r36J

* Ileated at 600"C, Proshchenko et al., 1966 BOGGS: OKANOGANITE I 14l

Ca, Al sitcate glasses for the rare-earth elements from point to point within the crystals. The low total (Drake and Weill, 1972), alblte for Na and Si, wol- is probably due to errors arising f1s6 using rar€- lastonite for Ca, hematite for Fe, synthetic PbSOofor earth standards which contain less of a given rare- Pb, rutile for Ti, and fluorite for F. Interelement ef- earth oxide than okanoganite (about 4 wt. percent in fects were corrected with a modified version of the the standard vr. up to 20 wt. percent in okanoganite). computer program EMPADR7 (Rucklidge and Gas- The empirical formula is (Na".ooCar.ooPboro) parrini, 1969). [(Y, Ce,Nd, La)r, rrCa,r6Fe,.u,](Si'' 2eTio.45) B644 An ion microprobe scan indicated the presenceof O., *Foror,which approximatesto an ideal formula of a significant amount of B, as well as minor amounts (Na,Ca)r(Y,Ce,Nd,La),rSLB2O2'Frov/rth Z : 3 for (lessthan 100 ppm) of Li, Al, K, Zr, Th, and U. It the hexagonal cell or Z : I for the rhombohedral also showedthe absenceof any signifisanl amount of cell. any other elements,including H and Eu. The BrO, content was determined spectro- Sinilar minerals photometrically with canninic acid on two samples A number of other rare-earth silicates containing of 8.5 and 13.5mg, u5ing a slight modification of the boron and/or fluorine are known. Many of these are technique of Ross et al. (1956) on a Becknan DU poorly described and most of them are metamict. spectrophotometer. The following is a brief comparison of eachwith oka- A summary of the analysesis presentedin Table 2. noganite. The crystals show no regular compositional 2sning rare-earth silicate, and only a slight random variation of a few percent Unnamed fluoro from Siberia, U,S,SR This mineral is the most closely related to oka- Table 2. Composition of okanoganite and a related unnamed Its cell dimensions,a : 10.68(4),c : rare-earth fluorosilicate from Siberia noganite. 26.90>4, are similar. The powder diffraction pattern

Siberian rare-earth (Table l) differs only in not showing many of the uKanogana ce Iuoro-s 11i cate* lower-intensity lines observedfrom okanoganite. The Na2O 2.74 2.1l chemical composition is also sinrilar (Table 2), but CaO 3.24 5.60 Pb0 0.63 differs mainly in containing phosphorus and alumi- ltrO 2.t5 num instead of boron (Proshchenkoet al., 1966).It Mco 0.20 the phosphorus and aluminum analog FeO r.60 may be either Fe2O3 3.69 of okanoganite or the same speciesif boron, alumi- tREE2O3 64.75 60.67 Bzog 3.1 num, and phosphorus do not occupy a separate site A1203 t.21 in the structure but only substitute for silicon. Pzos 2.83 TiO2 0.50 0.14 ThO2 0.93 M elanocerite,caryocerite, and tritomite Si02 L4. J) 14.00 Hzo 2.00 These three minerals are similar to each other and 11.15 7.85 are considered either as identical or separatespecies ro2.06 103.44 authors. They differ from okanoganite 4.69 3. 30 by different and Total 97.37 100. 14 by being enriched in the Ce-group lanthanides having lower REETO3contents, ranging from 43.5 to Yzo: 20.46 I4 .01 56.3 weight percent. All are metamict and recrys- La2O 3 5.88 6.25 Ce2O3 15.42 I3.71 6llize on heating in air to a mixture of an apatite Pr2O3 r.83 2.37 Nd2O3 7.70 9.22 phaseand a CeO, phase.In one casea melanocerite Sm203 r.64 3.03 was shown to have a few weak lines of an apatite Gd2O3 < ,e 4, L9 phasebefore heating (Portnov et al.,1968). Tb2O 3 o.44 o.42 Dyzo: 2.08 3.52 Ito2 O 3 o.96 0. 85 SPencit e l:tritomite- ( Y)l Er2O 3 L.26 I. 70 Tn2O3 o.20 0,06 This speciesdiffers from okanoganite in having a Ybzo 0.79 I e l 1.34 lower REETO, content, ranging from 28.0 to 50.7 Lu2O3 0.81 ) weight percent,a higher SiO' content of from 16.8to I REE2O 3 64.75 60.67 26.4 weight percent, and a lower F content of from * Proshchenko et al., 1966 0.0 to l.l weight percent. Spenciteis metamict and n42 BOGGS: OKANOGANITE

recrlstallizsson heatingin air to a mixture of an apa- M. E. KazakovaandZ. T. Kataeva(1973) New occurrencesand tite phase and a CeO, phase,but may have originally data for spencite.Can Mineral., 12,66-'ll. crystallized with a hellandite structure (Hogarth et Mandarino, J. A. (1976) The Gladstone-Dale relationship-Part I. Derivation of new constants. al., 1973)or a datolite structure(Frondel, 196l). Can. Mineral., 14, 498-5U. - (197E) The Gladstone-Dale relationship. Part II. Trends Yftisite arnong constants. Can Mineral., 16, 169-174. - (1979) The Gladstone-Dale relationship. Part III. Some This mineral differs from okanoganite in having a general applications. Can. Mineral., I 7, 7 l-7 6. lower REETO, content of 50.7 weight perc€nt and is Plehcva, N. I., A. P. Denisov and N. A. Elina (1971)A new vari- in group orthorhombic. The partial chemical ety the of rare-earth fluosilicates. Materialy po Mheral- analysis, which ogii Kol'skogo Poluostrova, 8, 176-179. (in Russian) (not totals percent, seen; 87.31 does not show the presenceor ertracted from Mineral. Abstr.,7Ll453, 1974 arrd,Am.Mineral., absenceof BrO, (Pletnevaet al., l97l\. 62,396, 1977). Portnov, A. M., G. A. Sidorenko, V. T. Dubinchuk, N. N. Kuznet- Acknowledgments sova and T. A. Ziborova (1969) Melanocerite from the norttr Baikal Region. Dokl. Akad iVazk I thank William S. Wise for much help and guidance on this SSSX, /8J, No. 4,901-904. Doklady of the Project. Special thanks are due to James R. Hinthorne who per- Itransl. Academy of SciencesU.S.S.R, Earth Sci- encesSection, 185, lffi-lO9 (1969)1. formed the ion probe scan"Daniel F. Weill, University of Oregon, Proshchenko,E. G., N. G. Batalieva for providing the rare-earth glass microprobe standards, pete J. and A. V. Bykova (1966)A rare-earth fluosilicate from a Siberian pegnatite. yse- Dunn, Smithsonian lnstitution, for preliminary work on the min- Zapiski nyuznyi MineralogicheskogoObshchestva, eral and for identification of several of the associatedminerals, 95, 339-345. (in Rus- sian); Mineral. Abstr., lE-125, 1967. and Akira Kato, National Science Museum, Tokyo, for several valuable snggestions. Rosg W. J., A. S. Meyer Jr. and W. C. White (1956) Determina- tion of boron in fluoride salts. Lr.S. Natl. Teclu InJ Sen., References ORNL-2135. Rucklidge, J. and E. L. Gasparrini (1969) EMPADR YII, a Com- Drake, M. J. and D. F. Weill (1972) New rar€-earth elcment stan- puter Program for processing Electron Microprobe Analytical dards for electron microprobe analysis. Chem. Geol., 10, 179- Data. Depaftment of Geology, University of Toronto, Ontario. l8l. Stull, R. J. (1969) The Geochemls.tryof the Southeasteraportion of Dunn, P. J., R. C. Rouse,B. Cannon and J. A. Nelen (1977)Zek- lhe Golden Horn Batholith, Northern Cascades, ltrashington lzr;ritei a new lithi"m sodium zirconi.m silicate reLatedto tu- Ph.D. Thesis, University of Washington, Seattle, Washington. hualite and the osumilite gtottp.Am. Mineral.,62,416420. Frondel, C. (1961) Two yttrium minerals: spenciteand rowlandite. Can Mineral., 6, 576-581. Manuscript received,December 28, 1979; Hogarth, D. D., H. R. Steacy, E. I. Semenov,E. G. proshchenko. acceptedfor publication, May 7, 1980.