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American Mineralogist, Volume 60, pages 566-573, 1975

Armalcolite-Ti-Phlosopite--Analcite-Bearing from Smoky itutte, GarfieldCounty, Montana

Dlutrtlr Vnlnn

Laboratoire de Pbtrographie, Uniuersitb de Paris VI, 4, place Jussieu, 75230 Paris Cedex 05, France

Abstract

Lamproitedikes and plugs occurringnear Jordan,Montana, contain highly unusual assemblagesof three major types:(l) sanidine,armalcolite, and alkali amphiboles (potassiumrichterite and potassiumriebeckite); (II) armalcolite,Ti-, diopside, olivine (altered),and sanidine;(III) armalcolite,Ti-phlogopite, diopside, olivine (altered), analcite,and glass.These rocks are low in Al2Os,rich in TiOr, and extremelyrich in KzO. They may be relatedin origin to the TiOz-and KzO-richultramafic rocks associated with the Montana diatremes.

Introduction surroundedby type I-a fine grainedassociation of sanidine,armalcolite, and alkali amphiboles,with The Smoky Butte intrusiveshave beendescribed abundantinclusions of sedimentaryrocks. by Matson (1960),where pertinent field data and a MineralogicalDescriptions summaryof previouswork can be found. The out- Sanidine crops of thesepotassic lavas are located8 milesdue west of Jordan (Montana),between Smoky Butte The only feldspar found at Smoky Butte is Creekto the north and thejunction of Big Dry Creek sanidine.It is presentin typesI and II. In type I it and Lone TreeCreek to the south.The nearesterup- representsthe greatestpart of the rock, occurringas tive rock, a nepheline-haiiynitealn

for the mostpart to the potassiumrichterite group, but someare potassiumriebeckites. Potassiumrichterites have been reportedfrom a number of lamproites(Prider, 1939; Hernandez- Pacheco,1965; Carmichael, 1967) and from certain minettes(Velde, 1965; Nemec, 1973); the host rocks for both of theseoccurrenced have very low sodium contentsand hyperalkaline characteristics. Potassium richteriteshave also been reported in nodulesfound in (Erlank and Finger, 1970; Aoki,1974). Experimentalwork by Huebnerand Papike(1970) hasshown that complete solid solution exists between sodium and potassiumrichterite end-members at I kbar waterpressure, between 775 and 850"C. Ftc. l. Phlogopitephenocrysts and clustersof skeletalsanidine The potassiumrichterites from Smoky Butte are crystalsin a type II lamproite. almostcolorless in thin section,being slightly pinkish alongB and very paleyellow along 7. This unusual trivalentiron contentof lunar armalcoliteis thought optical characteristiccan probably be related to to be zero, on the groundsthat the mineral is in their relativelylow iron contentcompared to other equilibrium-or at leastcoexists with-native iron. reportedmembers of the series.Potassium richterite The mineralfrom Smoky Butte has low FerO,and appearshere as a late crystallizingphase, occurring high MgO and TiO, contentcompared to most ter- mostlyin vugs.Sometimes it is rimmedby a thin zone restrialpseudobrookites (Smith, 1965; Rice, Dickey, of very strongly pleochroicamphibole (purple to and Lyons, 1971;Anderson and Wright, 1972).It dark prussianblue) towards the interiorof the vug. has, consequently,the closestcomposition to the Analysesreported in Table2 indicatethat this zone lunar armalcolite thus far reported in terrestrial has the compositionof a potassicriebeckite. This rocks. It could aptly be named ferri-armalcolite, showsthat potassiumriebeckite can in fact existin rather than magnesium-richferro-. nature.However, the rarity of hyperalkalinepotassic Figure 3 shows the position of lunar armalcolite, rocks, and the usual presenceof calciumin these Smoky Butte ferri-armalcolite,and Hawaiian rocks,can explainwhy potassiumriebeckite has not pseudobrookiteon a (Ti,Si)Or-(Fe,Mg,Mn)O-(Al, yet beenreported. Its occurrenceas rims on crystals Fe'+r)O3diagram (after Smith, 1965).The cell in vugs suggeststhat it could have formed by data, obtainedfrom an X-ray powder diffractogram precipitationfrom the vaporphase, similar to certain usinga programwritten by C. W. Burnham(1962), occurrencesof acmite (seefor exampleSmith and Lindsley,1971). Tluls l. Microprobe Analyses of Sanidine, Armalcolite, Ti-Phlogopite, Diopside, and Glass from Armalcolite Types II and III Lamproites The name armalcolite(Anderson et al, 1970)has Sanidine Atulcolite Ti-Phlogopite Diopside GLass been proposedfor a pseudobrookite-likemineral cenEet Edge with thegeneral formula Fe2+o.uMge6Ti2O6 found in a sio2 65.20 38.33 40.79 54.72 55.93 numberof samplesbrought back by the Apollo I I Al203 16.53 11.40 8.89 0.17 8.87 mission.Pseudobrookite is presentin most samples Ftzo3 2 -54 g.zo* from the FeO 20.28- :.za* 3.59 5.53 SmokyButte area. In typeIII rocksit occurs Mgo 11.68 19,18 17.25 t7 .56 5.25 as euhedralcrystals 0.03 by 0.3 mm (Fig. 2). These CaO o. o1 o.o2 0.o3 o.78 crystalsare not opaque,showing a faint purplishtint Na2O 1.14 o.28 0.34 0.30 1.10 K2o 14.49 10.52 10.52 4.14 in thin sectionand a weak birefringence.Table 3 MnO 0,15 gives the chemicalanalysis for the pseudobrookite lio o.33 61.56 2 11.21 I 1.O5 0.99 2.21 from type III rock. The structuralformula is: Ct203 + + (Til.s0Sio.0aXAlo.oaCro.o2Fe8o.ro)(Fe2 o.rrMgo.ur)Ou Total 100.28 102,06 96.83 98.13 100.29 93.11 Its generalcomposition corresponds to that reported for lunar armalcolite, except for the presenceof x indicates total Fe calculated as Fe2o3 or Feo *x totaL includes 4.7O7, iqnition loss,detemined on trivalent iron in the Smoky Butte specimen.The a sMlI sanple of 568 DANIELLE VELDE

TABLE2. MicroprobeAnalyses of Alkali Amphibolesfrom In lunar rocks (Haggerty et al, 1970) or in Type I LamproiteStructural Formulas Computed Hawaiian (Anderson and Wright, 1972) followingCzamanske and Wones(1973) pseudobrookiteis alwaysmantled by ,unless it occursin anotherphenocryst. In the SmokyButte Potassic Richterites Potassic RiebeckiEes intrusives,microprobe analyses for Fe, Mg, Ti, Cr, to be homogeneousand un- si02 53.19 s3.35 50.59 49.90 and Mn show armalcolite

At^o^ o.47 0.22 o.04 o.05 zoned(a representativemicroprobe analysis is listed FeO 3.66* 4.09* 29.50* in Tablel). Mgo 19,56 20.12 t,5r 2.67 The place of armalcolitein the crystallizationse- CaO 8.87 1.29 0.06 0.10 in- 'l quenceis of importance.In the Smoky Butte 6.41 ,o4 Na2O 3.90 3.87 trusives,armalcolite is foundincluded in clinopyrox- K2o 3.96 4,16 4.76 4.7L in somemica phenocrysts,but neverin the Tio2 3.45 3 . 43 4. 50 enesand olivines. This indicates that it crystallized after Total 91.O7 96.52 94,49 91.ffi olivine, and before some (if not all) of the Ti- pressure, si 7.626 8.014 1.973 phlogopite.In lunar rocks at atmospheric AL o.080 0.037 o. oo9 armalcoliteis the first phaseon the liquidus,followed Ti o.294 o.287 o. 018 (Akimoto et a/, t (teL.) 8.O00 8.000 8.014 8.OOO by clinopyroxenesand then olivine AI o.oo7 1970).This same relation was also reported by 0.439 o.492 4.O44 3.941 with 6.7to l0 Mg 4.180 4.3L4 0.356 o,622 O'Hara et al (1970)for compositions Ti o.078 o. o84 o.536 o.428 percentTiOr. At pressuresabove 20 kbar, no Fe-Ti > (M.-M^ ) 4.691 4.890 4.947 4.99r It oxidesare formed. Further, the Mg/Fe ratio of ar- 7.362 t.124 o.009 o. 017 NA 0. 638 o.876 1.988 1,983 malcolite decreaseswith decreasingtemperature, > (Ir4) 2.OOO 2.000 1.997 2.OOO from 0.81at l200oCto 0.59at ll50'C at I bar;at Na 0.445 o.204 o.197 I125"Carmalcolite is replacedby ilmenite(Akimoto K o.724 o.764 0.963 o.959 et al, 1970).The Smoky Butte armalcolite,with a ) (A) r.169 o.968 o.963 1.156 Mg/Fe ratio of 0.60,would then havecrystallized at * indicates total Ee calculaced as FeO the lower pressureand temperaturerange of its stability in the chemicalsystem in which it is found. are quite comparableto thosefor lunar armalcolite or for syntheticarmalcolite (Anderson et al, 1970). Analcite Valuesfor Smoky Butte are a : 9.749(9)A; b : Analciteoccurs as euhedral microphenocrysts (Fig. 10.026(12)A; c : 3.73s(8)A; V :365.0s7(791)A3; 4) quite similar in aspectto the leucitein the Wyom- for lunararmalcolite they area:9.743(30) A;6 : ing wyomingites (Carmichael, 1967). 11 is not 10.024(20)L; c : 3.73s(30)A; V : 36s.077(619)48, birefringent,a fact which probably explainswhy it numbersin parenthesesbeing the estimatedstandard has beenmistaken for leucite(Matson, 1960), since errors. the Wyoming leucitesare also isotropic.Analcite is found only in type II and type III rocks.In type II rocks,rich in sanidine,there is little analcite;however in type III samplesthe glassis abundant,and the analciteis freshand homogeneous.It shouldbe noted that, in Smoky Butte, analcitealways coexists with glass. Using CuKar radiation, the 639 reflectionfor this analcitewas displacedby 1.87"relative to the 331 reflectionfor the Si standard, indicating a Si-rich composition. This point falls outside the domain studiedby Liou (Fig. 1, 1971)and wouldcorrespond to a crystallizationtemperature below 350"C' Ac- cording to data given by Peters,Luth, and Tuttle (1966),the molar ratio SiOz:NazOwould be 4.5. Flc. 2. Armalcolitecrystals in a glassyanalcite-rich groundmass Qualitativeanalysis with the electronmicroprobe in- of type III lamproite. dicatesthe absenceof potassium. LAMPROITES FROM SMOKY BUTTE. MONTANA s69

As can be seenfrom the C.I.P.W. norms (Table 4), Trsle 3. ChemicalComposition of Armalcolite, the Smoky Butte rocks are not undersaturatedwith Ti-Phlogopite,and Diopsidefrom Type III Lamproite respectto silica. Consequentlythey should contain alkali feldspar and no analcite, and indeed the Alrulcolite Ti-Phlogopire Di.opside holocrystalline rocks do not contain analcite. It would then appearthat, in type III rocks,the analcite 'si02 o.96 39.09 53.24 crystallizedabove the stability field of sanidine and A1^O. o.88 7r.96 1.56 quenchingprevented the normal appearance of feld- F"203 1.45 4.04 2.25 spar and any reaction of analcite with the liquid. FeO L2.65 4.95 2.67 From available experimental data (Peterset al, 1966) Mgo lo. 53 19. 49 L6.31 we know that analcite can coexist with a liquid at CaO 20.90 pressures above 5 kbar, and, according to very Naro o.24 0.31 preliminary resultsby the sameauthors, above 3 kbar K2o 8.11 tr in potassium-bearing systems. The Smoky Butte MnO o.02 o.15 analcite,however, is silica-rich, an unambiguousin- Tio2 65.99 9.36 dication (Liou, 197 I ) of a low temperatureof crystal- po o.27 o. 08 z) lization. It seemsthen logical to considerthat a high ct203 o.67 temperature phase crystallized first but was replaced, o,56 at low temperature, by silica-rich analcite. This "2" H2o - o. 04 primary phasewould have beencubic on the basisof morphological considerations.Its most likely identity Tota I 99. 08 99.55 is leucite, but it should be noted that in the glassy wyomingites leucite was not replaced by a low a Spanishjumillite mica,and as high as 7.8 percent temperature phase, nor did it invert to the low in a west Kimberley fitzroyite (as comparedwith temperature non-cubic polymorph of leucite (Car_ Prider'soriginal figure of 8.97percent). The contrast michael, 1967). An unlikely possibility is the initial betweenLeucite Hills compositionsand the Smoky crystallization of a carnegieite. A description of Butteone is probablydue to rock bulk composition, carnegieite crystals formed in experiments (Bailey the LeuciteHills volcanicscontaining half as much and Schairer, 1966) in a purely sodic system as TiO, as do thoseof SmokyButte. "typical rounded octahedra" doesnot contradict this The cell dimensionsof the Smoky Butte Ti- possibility. phlogopiteare'. a : 5.323(7)L; b :9.163(3)A; c : Ti-Phlogopite (Ti'Si) 02 The phlogopite,perhaps the most obvious phasein hand specimen, is striking in thin section. Its pleochroism is strong, it is often zoned, and there seems to be a continuous variation in size from phenocryststo small crystals.In the phenocryststhe edge is more intensely colored than the central part. The extinction angle can be as large as 5o and twin- ning with an (001) twin plane is frequent. Micro- phenocrysts show the same optical characteristics (Fig. 5). The bulk analysisof the phlogopite is listed in Table 3, and representativemicroprobe analyses of the outer and inner zonesare presentedin Table l. The structural formula is: (Nao.6Ko.7s)Oro(OH)rISir.?6Alo.rrFe3+o.rrTio.ou] [Tio.noFe2+o.rrM gr.o.] (Fe,Mg,Mn)O (Al,Fe)2O3 It is outstandingbecause of its TiO, contentof 9.36 FIc 3. Composition of Smoky Butte ferric armalcolite (solid weight percent. Carmichael reported relatively low star) compared to lunar (solid TiO, values (from a armalcolite circle) analysis from 1.8 to 2.1 percent) in the Haggerty et al. (1970) and to a Hawaiian ferropseudobrookite phlogopitesfrom the Leucite Hills, but 5.9 percentin (open star) analysis (FPSB l3 in Anderson and Wright, t972). DANIELLE YELDE

Reid, 1970). In these instances,phlogopite phenocrystscan be interpreted as high pressure phases.The conditionsof crystallizationfor the latter mica were estimatedat I109'C and 24.2 kbar (Dawson et al, 1970). Titanium substitutionsin phlogopitehave recently been studiedexperimentally. Robert (1973)found that the 2 silv, Mgut : 2 AlIv,TivI substitutionis maximum at low pressures(1 kbar) and relatively high temperatures(1000"C). Forbes and Flower (1974)investigated the substitulion2 Mg'I : TivI, E, and deducedthat it is favoredby high pressures and temperatures(up to 30 kbar)' Figure6 is an Al-Fe (total iron) + Mg-Ti plot of the availableanalyses crystals in a type III lamproite. Clear prisms Frc. 4. Analcite including those of of diopside, armalcolite (black) and groundmass phlogopite are of titanium-bearingphlogopites, also visible the Smoky Butte (from Tables I and 3) and five other analysesof their grain centersand 19.985(9)A; fi : 94"54'(38');V : 971.2(1.2)43, edges.The two trendscorresponding to the two types numbersin parenthesesrepresenting the estimated of substitutionsmentioned above have also been standarderror. Thesevalues are comparablewith indicated.It is obvious that thesetwo substitutions those reported by Yoder and Eugster(1954) for a can accountfor the compositionsof the micasfound natural 2M phologopite.However, they are small in basaltsand in the garnetlherzolite, but they alone comparedwith a numberof dimensionsreported for cannot explain the compositionof the low alumina naturalphlogopites from lamproites(Velde, 1969). phlogopiteswhich seemto define a seriesroughly The only other micasthus far reportedwith such pa.uit"i to the join phlogopite-KrMg.TiAl2si.O2o high titanium contentsare phenocrystsin basaltic (OH).. In the seriesof naturalphlogopite composi- lavas (Flower, 1969; Velde and Coulon, un- tions,Si is closeto 6 ions per formula,but alumina published),or crystalsin mica-garnettherzolite in- is alwayslower than 2, evenin titanium-poorphlogo- cludedin an ankaramiticlava (Dawson. Powell, and pites.It is necessarythen to considerthe substitution of iron for tetrahedralsilicon. The formulaKr(Mg' Tenlr 4. Chemical Compositions and C.l.P.W. Norms of Fe2+).Alr.uFes+r.rSi.Ozo(OH)nwould approximately SmokY Butte LamProites representthe titanium-freeend of the series.The titanium-richmicas (the Smoky Butte phlogopites for Typ" Type Type Type Type Type I II 117 I II IIT example)are alsolow in silicon(5.5 ions per struc- tural formula) and in this case,since iron contentis sto2 52.19 53.53 51.89 low, titanium probablysubstitutes also for silicon' 9.O8 9.05 Al2o3 9,04 compositionshave Fe2O:. 5.02 4.39 3.86 a o.22 Thesealumina-deficient mica Or 46.39 46.39 45.O9 3. 50 l.O2 1.31 nothing Feo 2.19 3.OO 4.oj not yet beenstudied experimentally, so that MgO 7.98 7 .74 7.90 6.O4 11,74 11.10 stability.However, judg- Di 15.26 5.24 6. 18 canbe saidconcerning their 4.90 4.43 En 12.80 16,95 16.81 existenceas phenocrystsin nodulesin He 2.93 0,33 0.02 ing from their 1.93 L,91 Na20 1.14 I1 7.56 2.33 2.94 kimberlites(Aoki, 1974) andin hypabyssalrocks. they *zo 7.85 1.85 7.63 Tn 2.40 7.38 2.04 Pf 1.70 pressures. 0.o8 o.08 shouldbe stableboth at high and low Mn0 o.08 o.48 0.48 o.55 'Iio 4.96 5.23 5.11 2 Clinopyroxenes P^0- o.22 0.22 o.25 Ba0 o. 69 0.77 o.88 Clinopyroxenesappear as euhedral crystals which H2O + o.95 2.69 4.O5 sometimescontain glass inclusions.Chemical Hzo - o.54 1.12 analysisby wet chemicalmethods shows their com- Total 99.06 100.72 99.7 5 positionto be closeto that of diopside,quite com- Cu 25 28 22 Ni 600 415 405 parableto the analysesreported for clinopyroxenes Zn a1 a1 a2 Sr z,1oo 2,790 2,950 from the LeuciteHills volcanics(Carmichael, 1967). The structuralformula correspondingto the analysis listedin Table 3 is: LAMPROITES FROM SMOKY BUTTE, MONTANA

+ [A lo.orFes o.o6Fe2+6.s6M go.ssCae.62Tie.eaNao.or] (sil.eoAlo.ol)o6

Microprobeanalyses (see Table l) indicatethat the Si contentwould in fact be closerto 2 ions, and the alumina contentis slightly overestimatedin the wet chemicalanalysis. Glass Attempts have beenmade to determinethe com- position of the yellow glasspresent in type III rock with the electronmicroprobe. Results have shown consistentlylow totals (around 9070).Although re- producible,they cannot be consideredtotally ac_ curate. Loss on ignition was determinedon an isolatedfraction of the glassand found to be 4.7 per- cent. It is possiblethat the glassis enrichedin ele- ments such as barium and strontium,which were FIc. 5. Zoned phlogopite,with inclusions,in an analcite-rich groundmassof type III lamproite. not soughtfor but areabundant in the wholerock. A representativecomposition (the glassproved to diffractograms,which also indicate the absenceof be very homogeneous)is reportedin Table l. It analcite. differs from that of a wyomingiteglass determined The type11 rock is composedof phlogopite,diop- by Carmichaelmostly in its potassiumand calcium side, altered olivine, armalcolite,and abundant content.Leucite is a phenocrystphase in the wyom- elongatedcrystals of sanidine(Fig. a) which, with ingite, and as a result the glassis depletedin potas- someyellowish glass, form most of the groundmass. siumrelative to the bulk rock(2.69Voagainst 9.69Vo). Pseudomorphsof similarshape and sizeas analcite On the other hand,the crystallizationof diopsidein crystalsin type III are present.They resemble, the Smoky Butte rocks depletedthe glassin CaO, whereaswyomingites contain no diopsidepheno- crystsand the glassis calcium-rich. PetrographicDescriptions The type 1 rock is extremelyfine-grained and in- 'homogeneous. It is gray in hand specimenwith no mineral distinguishablewith the naked eye. Inclu- sions of sedimentaryrocks (lessthan a centimeter in diameter)are abundant.They are mostly sand- stoneswith varyingamounts of a phyllite-richmatrix. Theseinclusions never show any alterationor meta- morphism. Microscopically,the only visiblephases are poecili- tic, poorly formed crystals of phlogopite, quartz grains, barite, calcite, and alkali amphiboles.The amphibole,for the most part potassiumrichterite, FIc 6. Plot of observed natural phlogopite compositions occursin vugs;potassium riebeckite forms the apices comparing Al-Ti-(Total Fe + Mg) atomic proportions. Line A is the substitution studied experimentally by Robert (1973), of the richteritecrystals, or smallindependent line B prisms that studied by Forbes and Flower (1974). Crossesare micas from in the fine-grainedgroundmass of the rock. The vugs nodules (Aoki, 1974);triangles, micas from lamproites are filled by calcite,barite, and quartz in variable (Carmichael, 1967), solid triangles representing phlogopites from proportions.Armalcolite is abundant as minute the Leucite Hills; solid circles, phlogopites from Smoky Butte; crystals;priderite (identified by its opticalproperties) open square is a mica from a (Flower, 1969); open circle represents accompanies 4 analyses of mica phenocrysts in a sardinian basalt the amphiboles.Sanidine, forming the (Velde and Coulon, unpublished); solid squares are phlogopites greatestpart of the rock, was identifiedby X-ray from a garnet lherzolite (Dawson et al, 1970). 572 DANIELLE VELDE however,the alteredleucite crystals described in west In spite of thesedifferences, any satisfactoryex- Kimberleylamproites (Wade and Prider, 1940). They planationof the origin of the LeuciteHills volcanics are mostly composednow of mixturesof sanidine, could probably be appliedwith little, if any, change montmorillonite,and rninoranalcite, the turbid ap- to the Montana rocks. Available hypotheseshave pearancenoted in the Kimberley specimensbeing beenreviewed at lengthby Carmichael(1967) and quite conspicuous. subsequentisotopic studies of all knownexamples of The type III rock containsolivine, usually com- potassium-richlamproites and Montana diatremes as pletely replaced by pale green montmorillonite, well (Powelland Bell, 1970)have failed to provide zoned phlogopite, clinopyroxene,analcite, and ar- any better lead in determining the origin of malcolite in a pale yellow glass. A few sanidine lamproites. crystalscan be found with the usual quench-crystal One should remember, however, the relatively morphology.The calculatedmode, using a least closespatial association of theSmoky Butte volcanics squaresprogram following the method describedby with the ultramafic rocks of kimberlitic affinities Bryan,Finger, and Chayes(1969) gives the following (Hearn, 1968). The latter are characterizedby percentages(weight percents): diopside, l3; analcite, phenocrystsof forsteriticolivine in a groundmassof l0; phlogopite,13; armalcolite, 3; and glass,61. monticellite and/or melilite, nepheline,phlogopite, Other rock types were found in thin sections perovskiteand opaques.Unless contaminated, they loanedby the Departmentof Geologyof Montana do not contain any clinopyroxene and their StateUniversity. Exceptional among them is a rock potassium-to-sodiumratio is alwayshigher than one. made of potassiumrichterite, phlogopite, priderite, It is difficult to propose any kind of precise armalcolite, and sanidine with, possibly, some mechanismby which such an assemblage,so ex- wadeite.Such a rock should be somewhatricher in tremely undersaturatedwith respectto silica,would alkalis(i.e., potassium) and poorerin aluminathan produce a relatively low-temperaturemelting frac- the ones analyzedhere, but specimenswere not tion, enrichedin silica and peralkalinein character. availablefor study. Such a mechanismcould neverthelessexist, but all Table 4 gives chemical analyses,trace element we can sayat the momentis that suchliquids are not data, and C.I.P.W. norms for the threerock types likely to be generatedin the crust. At Smoky Butte that havebeen described. It is obviouswhen one con- their origin would then haveto be very deepindeed, sidersthe mineralogicalcompositions listed above, sincethe crust in this particulat zoneof the western and the chemicaldata, that such rocks can only be United Statesis at least45 kilometersdeep (Asada groupedunder the generalterm of lamproites,that is and Aldrich, 1966). volcanicor hypabyssalrocks with an alkali- (mostly Acknowledgments potassium)and magnesium-rich composition (Niggli, WesternReserve 1923;Wade and Prider, 1940,p. 50). The Montana I am very gratefulto Dr. John Hower, Case who gaveme the opportunityto studyrocks sampled poorer in University, rocks are considerablyricher in TiOz and some7000 miles away from my presentresidence, to R. E. Matson, KzO than the LeuciteHills volcanics.Their chemical MontanaBureau of Mines,who kindly sentme specimens from the compositionis close to that reported for the Smoky Butte quarry, and to G. Thompson,Montana StateUni- Australian lamproites, but the differencesin versity,who loanedme a numberof thin sectionsfrom various mineralogicalcompositions preclude the use of the parts of the outcrop. specificnames defined in west Kimberly. References AKrMoro, S. I.. M. Ntsutrlwn, Y. Nlrlruune, I. KusnIno, nxo Conclusions T. Klrsunl (1970)Melting experimentsof lunar crystalline The Smoky Butte area representsanother occur- rocks.Proc. Apollo tl Lunar Sci' Conf l,129-133. T. E. BuNcs, E. N. CeurnoN,S. E. HAG- renceof peralkalinepotassic eruptive rocks. Though ANoBnsoN,A T., csR.rv,F. R. Bovo, L. W. FtNcrn, O. B. Jerrans,K. Krtl, M. similarin many respectsto the volcanicsdescribed in Pnnz, P. Reuoonr, lNo A. El Gonnsv (1970)Armalcolite: A the Leucite Hills, they differ on the following newmineral from theApollo I I samples.Proc. Apollo I I Lunar grounds:high or very high TiOz contents,expressed Sci.Conf. l' 55-63. by the presenceof Fe-Ti oxides;abundance, in cer- -, ANDT. L. WRIcHT(1972) Phenocrysts and glass inclusions mixingof basalticmagmas' an Si-rich analcite,and absenceof and their bearingon oxidationand tain types, of volcano,Hawaii. Am' Mineral 57' 188-216. be com- Kilauea leucite;absence of any basictypes that could Aoxr, K. (1974)Phlogopites and potassicrichterites from mica paredto membersof thc madupite-orenditeseries of nodulesin south African kimberlites. Contrib. Mineral. Petrol' Wyoming(Carmichael, 1967). 48. l-7. LAMPROITES FROM SMOKY BUTTE. MONTANA 573

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