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Contents : THU AMERICAx JOURNAL M INERALOGIST SOCIETY OF AMERICA OF THE MINERALOGICAL Vo . tt4 JANUARY-FEBRUARY 19s9 Nos. 1 and 2 SECOND OCCURRENCE OF FERSMITE Laboratory Bureowo.f H. D. HBss aNo H. J. Tnuuroux Petrographic Mines fl . S. Deportmentof the Interior Albany Oregon. Alsrnacr Fersmite (Ca Ce Na)(Cb Ti Fe Al)r (O OH F)6 occurs as small anhedral inclusions and intergrowths with a tantalum-free columbite occurring in Ravalli County Montana. Chemical and crystallographic data along with the physical and optical properties agree in general with those given in the original description of fersmite from the Ural Mountains of Russia. X-ra1' difiraction data not given in the original description and more specific opticai data have been determined. INrnooucuoN Fersmite is a rare calcium columbate of the ABzOo group (Ca Ce Na) (Cb Ti Fe AD (O OH F)6 first describedfrom the pegmatitesof the Vishnevye Mountains Central Urals Russia by Bohnstedt-Kupletskayaand Burova (1946). the first recordedoccurrence The new locality for fersmite representing in North America and apparently only the second reported occurrence in the world is the Dark Star claim in sections3 and 4 T4S R22W Bitterroot Base Line Ravalli County NIontana. The prospect is in the east slopeof the Bitterroot Mountains approximately ruggedly dissected five miles south of Alta Nlontana and is easily accessibleby highway chiefly of schists roads.The region is composed and Forest Serviceaccess and gneisses believed to have been originally Belt-seriesargillaceous and calcareous sedimentsof Precambrianage that were metamorphosed during the introduction of the Idaho batholith (Ross 1950).Intermittent amphibolite quartzite and thin-bedded marble also are present. Rhyolite and pegmatite dikes crosscut and intrude the metamorphic complex in a number of areas. The fersmite describedherein occurs as small anhedral inclusionsand with monazite intergrowths with a tantalum-free columbite associated ancylite barite qvartz and apatite in a fine-grainedbuff-colored marble. The bed rangesin thicknessfrom approximately 1 to 6 feet and reportedly can be traced for approximately 700 feet along the surface.Accord- 2 H. D. HESSAND H. T TRUMPOUR ing to Sahinen(1957) the strike of the marble is N. 67+"W and the drp is 77'NE at the surfacebut straightensto vertical near the bottom of a 12-footcut. As shown in Fig. 1 the columbite along with intergrown fersmite occurs as well-defined blebs and irregular massesranging up to 2 inches across.The microcrystallinestructure of these black masses and particularly the close relationship of the fersmite to columbite is illus- Frc. 1. Photograph of selectedspecimensillustrating the occurrence of the black columbite masses which contain the fersmite. trated in Fig. 2. Monazite is observedonly as small sparselydisseminated anhedralinclusionsin the columbite masses and can be recognized with the unaided eye in contrast to the black host mineral. Conversely the the ancylite is not directly associated with the columbite but rather occurs as a fine-grained pinkish material associated with the carbonatehost rock. The presenceof these columbium and rare-earth minerals-ordinarily regardedas being of granitic or pegmatitic origin but here occurringin a metamorphosed limestoneof probably sedimentaryorigin-represents a unique occurrence. It alsois of interestto note that high-purity columbite concentrates analyzed by optical ald x-ray spectrolraphicmethods at the Albany Oregon Iaboratory of the Federal Bureau of lVlineswere found to contain no tantalum. The tantalum-free nature of columbite from the Dark Star claim originally was reported by Sahinen (1957) SECONDOCCURRENCE OF FERSMITE 3 on the basisof analysesmade by the X ontana Bureau of Mines and the U. S. GeologicalSurvey. However the black homogeneous-appearing columbium-bearingmasses were describedby Sahinenas being "stubby prismatic crystals of columbite as much as two inches across " and no mention rvas made of the intimately intergrown fersmite. Frc. 2. Plane light X45. Photomicrograph of columbite massesshowing the relationship of anhedral fersmite (gray high relief) to subhedral columbite (black) and interstitial calcite (white). The l Iontana fersmite first was noticed in January 1954 during a routine mineralogicalexamination of a prospector's sample submitted by Louis Erickson Corvallis X ontana to the U. S. Bureau of lllines Petrographic Laboratory at Albany. At that time R. E. Lubker the laboratory geologistexamining the sample called the authors' attention to a small quantity of a dark brown translucent mineral which he observed in the nonmagneticfraction of crushed material passedthrough the Frantz isodynamic magnetic separatorat 1.5 amperes. When the mineral could not be classifiedby r-ray difiraction analysis a more thorough study and literature searchwas made to determine the possibility of a new mineral species. ft was through this detailed study and subsequenttests made on a suite of selectedsamplessupplied by 4 II D. HESSAND H. J. TRUMPOUR Louis Erickson that the unidentified mineral was found to have the propertiesof fersmite as describedby Bohnstedt-Kupletskaya and Burova (1946). Unfortunately the original description of fersmite lacked r-ray diffraction data and attempts to obtain identified samples for comparisonpurposes were unsuccessful. However the chemical physical and optical propertiesand limited crystallographic data listed correspond so closelywith the material from Ravalli County that the relationship seemsunquestionable. Cnvsr qr r ocRAPHY llontana fersmite occurs as small anhedrai inclusionsand intergrowths with columbite. This plus its extreme brittleness made it impossibleto obtain individual crystalssuitablefor detailedstudy with the optical goniometer. However through considerablesearch and effort severaiimperfect crystalsand crystal fragmentswere isolatedpermitting limited single-crystal study. Study of thesefersmitegrains indicatesthat the mineral is orthorhombic in crystallization and belongs to the bipyramidal class. The few distinct crystals observedmeasurefrom 0.5 to 1 millimeter across while the predominant anhedral forms are somewhat larger. The habit is prismatic with the unit prism (110) predominating and lesscommonly tabular parallel to (100). Macrodome and macropinacoidmodifications also are observedon some of the crystalline grains. The prism facesare striated and severalcrystal fragments showedparting parallel to (100). T h e a x i a l r a t i o a s d e r i v e df r o m : r - r a ys t u d y i s a : b ' . c : 0 . 3 8 1 : 1 : 0 . 3 4 6 which compares w i t h t h e " a p p r o x i m a t er a t i o " a : b : c : 0 . 3 7 7 : 1 : 0 . 3 5 6r e ported by Bohnstedt-Kupletskaya and Burova (1946) on the Russian fersmite. UNrr Cnr.l eNn Spacn Gnoup The unit cell dimensionsof the l ontana fersmite were obtained with NIoKa radiation using a cylindrical camera. Following the same technique the cell dimensionsof the associatedcolumbite also were determined to illustrate the rather close similarity of these two intimately associated minerals. The spacegroup of fersmite was found to be the same as for columbite and tantalite D21 1a Pbcn. The cell dimensions obtained for the fersmite and associated columbite are as follows with the order of listing in conformance with the fnternational Tables for X-ray Crystallography: Fersmite a " : 5 . 7 6 4A 6":15.09 A c": 5.232A Columbite 'Ihe a": 5.730 A b":14.n8A c": 5.082 A OF FERSMITE SECONDOCCURRENCE X-naY PowlBn DrllnacrroN Der t 5 The original description of fersmite reported by Bohnstedt-Kupletskaya and Burova did not include powder diffraction data and therefore a comparison could not be made. The powder diffraction data obtained for the Montana fersmite using a Norelco Geiger Counter Spectrometer and CuKa radiation are listed in Table 1. T clle 1. X-Rev Pown lnou Revelr t Spacrrc D.lr.t ron FBnsurre CouNrv MoNrl.Ne CuKa radiation d (meas..) d (calc ) dd (meas.) r/h 6 9 2l 9 100 a + 7 8 l4 1 1 1 5 4 1 5 hkl (calc.) I/Io 7.449 5.345 J.loz 7. 5 4 5. 3 8 J.tt J.++ 020 110 (ttt t.626 1.580 I.JJ/ 1.62 1. 5 8 1. 5 4 1. 5 3 1.52 1.51 1.49 1.48 1.46 .43 1. 3 8 1. 3 8 l.J/ 6 4 2 15 (zrc 350 043 I o+o t2l 131 200 220 002 060 o22 102 lJ I 3.427 3.049 2.864 2.684 2.606 2.5r4 2.493 2. 3 8 s z.Jol 2.279 2.247 2.t45 2.117 2.087 2.O0+ 1.967 1.929 t.916 1 .899 1.882 1.862 1.804 .789 t.786 3. 0 7 2. 8 8 2.69 2.62 2.52 2.47 2.38 2.38 2.27 2.26 !.TJ I.JZI 262 191 082 1 )') 1. 5 r 2 1. 5 0 2 1.489 1.482 t.476 t.427 1. 3 8 7 1. 3 8 0 1. 3 6 3 1. 3 3 4 .229 1.256 r.248 1.245 1.222 1.2r1 1.192 1.183 1 1.58 1.14.5 1.133 1.126 t.121 I.lo7 2 2 fo.ro.o 1281 2r3 332 . r 4 2 1 lsot zzs 061 LJI 2.tl 2.ro 2.01 7.94 I .93 1.91 1. 8 9 1. 8 8 1. 8 7 1. 8 1 1.80 t.79 1 aa 3 10 3 1 1 9 1 9 7 8 8 132 16t 241 142 251 202 310 080 ( 't't t 1. 3 3 1. 3 0 1.26 1.25 t.25 1.22 1.21 1.19 1. 1 8 l.t6 I.I) o 1 1 3 11 13 1 1 1 .' (nz i+st 333 183 343 144 204 154 064 480 392 462 JIT 370 4ll 352 42I 1 .1 1 . 0 4+l ')')') t52 232 330 .tt I r.77t 1.69r 1.629 (ozs I 331 tct t '"' 341 1 081 .t4 l.lJ r.70 1.63 rar I ( l.l2 1.11 1 521

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