American Mineralogist, Volume 60, pages 675480, 1975

ChemicalInvestigation of Pyrope Garnetsin the StockdaleKimberlite Intrusion,Riley County,Kansas

FnnNz Rosrt, EsnnHd\noBnnnMlNN, huo GroRc Atrlrsnugn Fachrichtung Mineralogie der Uniuersitiit des Sqarlandes, Saqrbrilcken, Germany

Abstract

The color variationsbetween 4l separatepyrope garnet fractions from the Stockdale kimberliteare causedby differingchromium concentrations.Two main seriesmay be dis- tinguished.Series I showsa widecolor range from paleorange to dark violet,corresponding to CrrOrcontent from 0.2to 13wt percent;the cell edge increases from ll.5ll to 11.647A. SeriesII is characterizedby light pink or redcolors, CrrO, values below 2.5 wt percent,ahd TiO, contentsgreater than 0.5 wt percent.The largercell edgesin SeriesII are causedby higher content of Fe3+, which is proved by reflectancephotometry and Mcissbauer spectroscopy.The quantitativedistribution of chromium in the Stockdalegarnets is representedin a variation diagram.

Introduction the calculatedformula induced Brookins and others Many kimberlitescharacteristically contain pyrope to reinvestigate the red garnet. Brookins' (1967) garnetswhich originate from garnet peridotite and analysisof red pyropeyielded SiOr,44.l l;TiO2,0.27; pyroxenite xenoliths, or are geneticallyrelated to AlrO3, 21.50; FerOt, 1.37; CrrO3,2.77; FeO,7.55", kimberliteitself. Investigationson pyrope garnets MgO, 20.57; CaO, 4.64; MnO, 0.37. Rosa and from kimberlitesby Nixon, Knorring, and Rooke Brookins (1966)determined ao to be ll.535A for red (1963),Nixon and Hornung(1968), Meyer (1968; pyrope and ll.558A for "green" pyrope. Brookins 1970),Sobolev, Lavrent'yev, Pospelova, and Sobolev (1967) concluded that, becauseof the high value of (1969),Reid and Hanor (1970),Meyer and Boyd the unit cell and refractive index, the "green pyrope" (19'72),and Gurneyand Switzer(1973) show colors may be even more chromium rich than the red ranging from pale orangeto red and dark violet, pyrope. Other garnetsfrom eclogitexenoliths in the causedby an increasingchromium content from I to Stockdale kimberlite have pyrope-almandinecom- 3 wt percentup to l0 wt percentof CrrO, and more. position and "appear unrelatedto the pyrope garnets These garnets have been defined as "chrome which occur as xenocrysts within the kimberlite" pyropes."Similar variations of pyropegarnets from (Meyer and Brookins, l97l). many Europeangarnet peridotiteshave been in- vestigatedquantitatively (Rost and Grigel, 1969; Methods Amthauer,Brenneis, Grigel, and Rost, l97l; Rost, Preparation Wannemacher,and Grigel, 1974). In Riley County,Kansas, 6 kimberlitediatremes About 20 kg of garnet-bearingkimberlite rock was are known (Brookins, 1970),among which the crushedand sievedto grain sizesbetween 0.3 and 0.8 kimberliteof Stockdalehas the remarkablecontent mm, and treatedwith dilufe hydrochloric acid to dis- of4 percentpyrope garnets (Eastwood and Brookins, solve carbonates and decompose serpentine and 1965;Rosa and Brookins,1966). Bagrowski (1941) other minerals.Heavy mineralswere separated by us- : had beenthe first to identify aspyrope a red mineral ing Clerici solution (D 3.5) and the garnetswere in the Stockdalekimberlite, previously believed to be concentrated by using a Franlz isodynamic "ruby spinel."Discrepancies in the analysisand in separator. This portion was then heated with hydrochloric acid (HCl: HrO : I :2) on a magnetic producing grainswith cleanand polished t Presentaddress: Professor Dr. F. Rost, FachrichtungMiner- agitor, thus alogie der Universit2itdes Saarlandes,D-6600 Saarbriicken. surfaces.Those garnet grains without impurities and F. R. G. inclusions were finally picked out by hand (enlarge- 675 676 ROST, BEERMANN, AND AMTHAUER

mentof binocularmicroscope 16-25) to obtainabout centrationin Tables| , 2, and3. Garnetswhich could 2l g of pure garnet. only be separatedin amountsof a few mg wereex- The discriminationof differentlycolored garnets is aminedby determinationof theircell edges (Table 4). necessarilysubjective. The authors,however, suc- By comparisonof the resultswith the cell edge ceededin selecting4l garnetsamples of like color- values, the pyrope garnets from the Stockdale termedfractions-in differentlots (SeeFig. l, Table kimberlitefall into two main series. s). Each garnetfraction groupedinto SeriesI (Table l) possessesa definite value for co;with minorexcep- Analytical Methods tionsao increases steadily from I1.521to 11.581A as garnet fractions totaling more than 400 mg Those weight percentCrrO3 increases from 0.46 ro 7.20. with Philips X-ray vacuum spec- were analyzed a Thosegarnet fractions grouped into SeriesII (Table For garnet fractions less than 400 mg, trometer. 2) atsohave a definitevalue for aobut, unlike SeriesI was to determineFeO, emissionspectrography used garnets,their TiO, contentsgenerally exceed 0.50 wt (Rost and Hausner, CaO, MnO, TiO2 and CrzOs percent.For them ao showsa lesserrange than for 1954; Rost and Grigel, 1964; 1969). The standards SeriesI, all but onebeing between 11.540 and 11.548 used were predominantly common international A. SeriesII garnetshave largervalues of ao when standards and mixtures of these. The accuracy of comparedto SeriesI garnetsof approximatelyequal was between2 and 6 percent, both methods estimated CrrO, content.The CrzOecontent of SeriesII garnet and its concentration. dependingon the element fractionsdo not exceed2.5 wt percent. were determined by using the Guinier Cell edges Garnetfractions 6, 18,and 20 in Table3 yieldtwo 10.10.4reflection method, measuringthe distanceof distinctcell edge values. Since one value corresponds garnet against 4.4.4. refleclion of pure silicon; the of to SeriesI and the otherto SeriesII, fractions6, 18, was A. Single grains were ex- accuracy 0.001-0.002 and20 areprobably mixtures of SeriesI andSeries II camera (Gandolfi, amined by using the Gandolfi garnets.Fraction 37 in Table 3 consistsof violet- 1967);the accuracywas 0.005 A. colored garnetsthat give a broad reflectionin the Results Guiniercamera and undoubtedlybelong to SeriesI. Chemical Composition of the Stockdale Garnets Both pyropesstudied by Rosaand Brookins(1966) garnet The analytical results for the various garnet frac- and Brookins(1967) belong to SeriesI; thered garnet tions are arrangedaccording to their chromium con- correspondsin CrzOscontent and cell edgeto fraction3l in Tablel. Wt On the basisof color and cell edge,the authors

L_l Seiles u favor inclusionof the garnetsin Table4 into SeriesI. 39 to 4lc compareto fractions38 I serles ]+ll mixed Thus fractions (Table l) and 37 (Table 3); they show the "alex- f_-] series t

Tlst-r L Analyses of Stockdale Garnets, Series I

Nr. SiO2 A12 Ot FeO MAo Cao Mno T1o2 ur2 ot

7 9.50 - b.oo o. J5 o.25 O.46 11.523 I 7 '90 - 5.Oo o.?) o.14 o.50 11.521 9 9.90 - 5.60 o. 44 o.22 O.52 11,52) rt 42.5 22.t+ 8.50 21.1 4.40 o.49 o.28 1.35 11.525 19 7.60 - 6.00 o.38 o.24 1.90 11.5)O 7,60 - 4.70 o.43 o.23 2.1O r1.531 7.50 - 6.00 o,42 o.25 2.1O r1,532 24 42.o 21.5 ?.45 21.4 4.45 o.45 o.2'l 2.18 11.533 6.7o - 5.80 o.43 o.65 2 .2o 11.5)4 29 42,O 21.4 7.53 20.6 I1.60 o. 54 o.14 2.)5 1r,532 3O 7.60 - 6.80 o,5J o.2J 2.35 11.533 41.6 22.2 7.65 21.4 4.45 o. 34 o.18 2.80 11.535 32 41.O 22.2 7.45 20.6 4.85 o.3) o.2o 2.85 11.539 33 4r.0 20,8 7.2O 20.4 5.40 o.52 o,12 4. oo 11 .546 - L1 Frdclion Nr 39 34 !+1.5 21.3 6.92 2o.o 5.40 o.51 o.17 4.t+5 11.549 (023 ||t%.1 J) 40.6 20.o 6.95 2o.o 6. oo 0. 70 o.l1 5.5O 11.56J 7.60 - 6.30 o.15 6.o5 t1.567 38 40.5 I 8.0 6.4o 18.2 7, OO o.65 o. 09 ?.2o r 1.581 012315678910111213 f, 41,3 ?1.) 7.55 o.47 o.26 3,18 WIok Cr20, Notes for Tables 2,3 and 4: Frc. l. Simplified histogram of the distribution of chromium con- Nr = number of garnet fraction tent in the Stockdale garnets. Series III : SeriesI plus Series II, - = oxides by spectrographical nethod not deternin€d fi = average composition of series mixed. PYROPE GARNETS IN KIMBERLITE INTRUSION

Teglr 2. Analyses of Stockdale Garnets, Series II* T,c.sI-r4. Cell Edge,Color, and EstimatedChro- mium Contentof SomePeculiar Garnets*

2 42-.O 22_.5 4.95 2O.2 4,80 o. 39 o.84 o.32 11.54o Garnet Cell^Edge Wt percent Lolor 9, oo 5.90 o.41 o.70 o,35 11.5J5 No. (A) Cr 4 1O.50 6,40 o.1+2 o. 54 o.42 11.544 ror* 5 8. 70 6.50 a.j9 o. 62 o,45 11.542 10 8. 70 6.OO o. l5 o. 64 o.75 11.545 1 Pale orange ll.51f 0.2 ll 8. lo 6. oo o.44 o. 84 1.OO 11.544 39 Dark violet 1l .595 d.5 OO 4.7o 9. o.3t r.20 11.54J 40 il il 1l.611 10.0 8. 70 6.50 o.39 o. 66 1.2O 11.544 r4 9.20 5.60 O.4l o .52 1..1o 11,544 +ra I I .631 il.9 16 7.?o 4.7o o.3a r.40 1i.5L3 4lb 72.4 17 1+1.8 21.5 8.1o 2o.z 5 ,oo o.35 o.86 1.46 11.545 1.r.637 1Z Z 7.60 5.50 o.4l o.90 2 . oo lt .54'l 4Ic tr.647 26 6 .80 6,oo o.42 o.6o 2.2o I 1.544 ?.60 6,20 0.43 o.50 2.20 11.547 x Cr'rO, uaLuee estimated bg ertnapoLation 28 41.6 20,8 7 .35 21.4 5.15 o.43 o. 84 2.)2 11.548 fr )11.8 21.5 8.50 2o.6 5.37 0,39 o.75 aeeor&tng to Figuz,e 3.

ReflectancePhotometry and MbssbquerStudies on andrite effect" (White, Roy, and Mck Crichton, StockdaleGarnets 1967). The reflectancespectra of 5 selectedgarnet frac- The histogramof Figure I showsthe quantitative tions (Fig. 2) may be interpretedas follows: (l) The variationof chromiumcontent in all garnetfractions chromiumcontent influences the color by the absorp- collectedin columnsaccording to the CrrO, content tion bandsnear 410 nm andbetween 560 and 570 nm. in stepsof 0.05- 1.0, 1.05-2.0, . wt percenr,etc. (2) Garnetsl7 and27 from SeriesII havea more in- The variation correspondsapproximately to a tensive absorption within the whole wavelength statisticaldistribution curve. range,especially between 450 and 510nm. The gar- nets of SeriesI in this rangehave higher reflectance Auerage Chemical Composition and Formulas of values.(3) In thespectra ofthe garnetsfrom SeriesII, StockdaleGqrnets a characteristicabsorption peak near 367nm occurs Takinginto accountthe weightportions of garnet which belongsto Fe3+in octahedralcoordination. fractions,the averagechemical composition of the This assignmentindicates higher content of Fe3+in single series has been calculated (Table 5). garnetsof SeriesII (Amthauer,1974). Differencesbetween Series I and II may be observed Finally, Mbssbauerstudies on 4 garnets,whose in the total contentof iron-determined analytically reflectancespectra are givenin Figure2, gavefurther as FeO-and in the higher titanium and lower information about the differencesof the Fe2+and chromiumcontent in SeriesII. Fe3+content in both main series.Although the deter- Accordingto the calculatedformulas, the garnets minationof intensityaccording to the peakareas of in theStockdale kimberlite, investigated herein, show Fe'+ and Fe3+demonstrates only a low absolutecon- a correspondingvalue of "pyrope" exceeding72 mole tentof Fe8+compared to Fe2+,the Fe8+value in gar- percent only insignificantly.The analytical results show characteristicdifferences between the elements Tenle 5. Average Composition and Formula of Garnets from the in the I position of the garnetformula. The higher Stockdale Kimberlite valueof Fe3+in SeriesII is of specialimportance and causestheir higher valuesof as.A dependenceof ao Weight% Si02 At203 FeO' lt4g0 CoO VlnO Ti02 Cr203 on the titaniumcontent is not evident. SeriesI 7750 t13 213 7L1 2057 526 049 016 350 SeriesII 1587 t18 216 850 2060 537 039 075 125 TlsI-s 3. Analyses of Garnets with Complex Composition* x 6/'0 t12 208 7.tE 2O3L 570 0U 0.26 1,15

5i02 -{12 0l Ieo MgO CaO MnO TiO2 Cr2 O, a I {Mg Fe,l:,co,r, Mn1), (Atr77 Fel; crn,Tio.), [(siss7At1 )04l3 11'521/ rr. o 3 6 11.30 6.zo o.t15 o.25 o.L5 11 .542 11',31/ I] (Mg Fefo-.Co136 Mnos )3(Alse Fe;; cr3 [(Siee )01] 18 / ' lv 4.80 o.rrl o.f8 r.80 rI s 6Ti2o) 2 3Ato7 3 11 .546 11 20 tr1.a 23.3 7,8o 21.4 4.80 o.42 o.48 1.97 '524/ x {Mgrr, Fefl]uCo,.t'4no )r[(SisB?AL1 11 .5q6 u r)r(Alur.Fel;rCr.,orTior, 3)04]3 11'562/ 40,6 14.7 5.60 19.8 6.45 o.50 o.rr 6.7o 11.5'19 *Totql *ln lron qs Feo the formulos some Fe2* recotcutotedos Fe3*. 4i.2 20.8 20.j4 fr 7-46 t.7o o.47 o.26 4.15 .* Elements in the swerol positions X,Y ond Z ore @lculotedto the sum 100 see footnotes to Table 2 x Averogeof gornets wath complexcomposition (Toble 3) 678 ROST,BEERMANN, AND AMTHAUER

Reflectonce

\-.. -s Tt \ \ \\,. Cr3*

\2^ -\ .?t----z -\J r /-..- ?2 ,<' \-!.---- 06 \-

05 I

Cr3' 04

-' '- '' t"3 29--- 235 ,l Series I \ 35-550 ,l 17----1t-6 'l \i Serres II

7OO 600 500 400 300 WovetengthInmJ Ftc. 2. Reflectance spectra of Stockdale garnets (Amthauer, 1974). net l7 (SeriesII) is nearly twice as large as in the gar- 1968), Rickwood, Mathias, and Siebert (1968) and nets of SeriesI (Amthauer, 1974).These discrepances Gurney and Switzer (1973,Table l) and the pyropes cannot be interpreted without further research. The from peridotites of the Middle European Basement results agree, however, at least relatively to the other described by Rost and Grigel (1969)'. These results presentedin this investigation on Stockdale similarities include (l) a "pyrope content" between garnets(Table 6). 70 and 73 mole percent, (2) a CaO content of at least 4 wt percent, and (3) a trend of cell edge values like Discussion that in Figure 3. Chromium contentsof pyropesfrom Series I pyropes from Stockdale kimberlite resem- garnet peridotitesof Bohemia and Austria reach 7.6 ble similar garnetsdescribed from other kimberlites percent CrrO, (Kleinpiichlarn, Austria) and 8.0 per- by O'Hara and Mercy (1963), Nixon et al (1963; cent Cr2O3(Drilling T 7 Linhorka, Bohemia) and ex- ceed the value which Reid and Hanor (1970) have Teslr 6. Results of M6ssbauer Investigation on Four Stockdale reportedin Bohemianpyropes ("3.2 wt percentCr2O3 Garnets in Mg-rich pyropes"). In the Stockdale pyropes of earnet Nr, 9 1'7 29 )5 SeriesI the chromium content attains ca 13 wt per- Series I II I II (garnet 4lc in Table 4); the highest chromium $ crrot o,52 1.46 2.)5 5,5o cent '11.523 ce11 edse (8) 11.545 11.532 11.56) concentrationof 17.47wt percentCrrOs in garnet K 47 from a south African kimberlite causedNixon and !l6ssbauer data Hornung (1968) to designatethis garnet as "knor- _^1 | "Lhat . 15 (mmlsec,, 1.u2 1.42 1.43 1.42 ringite." Theseauthors considerit probable PT ! e cuo neces- E { mmlsec, -3.67 -J.65 -3.65 -J.ot conditions such as obtained in the mantle are r?' sary for the formation of chromium-rich pyropes, ex- tsl (*r/.ec) o.44 o.42 o.45 o. 44 1+ Fe- oct ceeding 10 wt percent CrrOr." These conditions are f,- I mm/ sec , o,26 o.29 o,28 o. )2 e probably higher than in the deepest parts of an * n-2 94 89 94 93 Intensitvl- orogenic crust, where garnet peridotites may be FeJ+ t1 6 7 formed (Rost and Grigel, 1969).

I = IS isomere shift 2 Former publications about pyropes of this region, especiallyby 2 = quadrupole Ue splitting Czechoslovakian authors, are taken into consideration in this 3 = of peak areas (, o.5 Intensity relation *') paper PYROPE GARNETS IN KIMBERLITE INTRUSION 679

Chromium concentrationsin pyrope garnetsin_ higher supply of TiOz and a higher oxidationpoten- cludedin or closelyrelated to diamonds(Mever and tial. Boyd,1972 Sobolevet al,1969:Gurney and Switzer, The pyrope garnets "related to or included in 1973)do not exceedthe valuesin pyropeshitherto diamonds"show dn evidentlyhigher mole percentof reported. pZcondi_ This fact suggeststhat increasing Mg garnet than garnetsin an environmentmissing tions cause the trend towardshigher chromium con- diamonds; this percentagefluctuates between 75.1 tents in pyrope-rich garnets, but the amount of and 87.8(Gurney and Switzer,1973; an averageof 35 chromium availablefor an isomorphoussubstitution analysesgave 8l .2 molepercent), 78.1-86.3 (Sobolev in pyropes absolutelydoes not seemto increaseat et al, 1969;average of ll, 82.6mole percent),and greater depthsof the mantle,where diamonds origi- 81.9-88.9(Meyer and Boyd, 1972;average of I l, g6.5 nate. mole percent).Furthermore, these garnetshave a The garnets of SeriesII from the Stockdalekim_ negligiblecontent of titaniumand lower calcium con- berlite contain equal valuesof CaO and MgO (ca centration,which cancause the lowercell edge values 72 molepercent pyrope),but lowerconcentrations of of garnetsin Figure 3 (Meyer and Boyd, 1972). Pyropegarnets genetically connected with diamonds "are consideredto havea deeperprovenance than the magnesiangarnets commonly found as xenocrystsin kimberlite and in garnet peridotite xenoliths" (Gurney and Switzer, 1973).

-o- .' /,1b -o- . /,lo

610 -o- L 2/.8 . 11600 da -0- 590 ,' 39

580

570

560 ,/'o1 115s0

5/.0 '.iilJ!!: ,."|,n{n + UZUA 612o 530 ,",*$.{u, GL ts

-n4v+ + 520 46 69o GL2/,o 6L 25o 510

^ ltt' 012345678 J 10 11 12 13 1/. 15 16 17 1g Weight% CrrOt Ftc. 3. Cell edgesof the Stockdalegarnet fractions (series I and II) plottedagainst chromium content. For comparison,plots of other pyrope garnetsare added. (l) chromium-richgarnets from garnet peridotites: K I 9 and K I I I (Kleinpcichlarn,Austria); L 245(Drilling T 7, Linhorka,Bohemia) (Rost and Grigel' 1969).(2) Kimberlitegarnets: (a) BR ("red garnet",Brookins et al, 1966,1967;from Stockdale); (b) A 6 andA 4 (o'Hara andMercy, 1963); (c) E 9, E 10,and K47 (Nixoneral, 1963,1968);(d)c 9a,c 12a,GL l5e+h, G 20a,GL 24a, and GL 25a(Meyer and Boyd, 1972). 680 ROST.BEERMANITT, AND AMTHAUER

(1963) Acknowledgments NrxoN, P. H., O. voN KNoRRING,AND J. M. Roorr and associatedinclusions of Basutoland'lm' The authors would like to thank Dr. P. c. Franks, State fllb"tlit:: Mineral' 4t' 1090-l132' ceologicalSurvey, University of Kansas,Lawrence, runrur, *t o rhestudy *", i"";;;;;p: kindrysent the kimberlite sampres. ,n"rnoli'i";X,?1ilili:X"ltlr::;,":*::*\rf::::;"::, ported by the "Deutsche Forschungsgemeinschaft." lg33_1g40. References O'H,rn,r.M. J., rNo E. L. P. MEncv (1963)Petrology and petrogenesisof somegarnetiferous peridotites. Trans Roy. Soc. AMTHAUER,G. (1974\ Zur Kristallchemie chromhaltiger Granate. Edinb.65. 251-314. Dissertation, Universitht des Saarlandes, Saarbriicken. REro.A. M., ,txp J. S. Hrnon (1970)Pyrope in kimberlite.lm. -. G. P. BRENNETS,W. Gnrorl, rNo F. Rosr (1971) Uber M ineral. 53. 1374-13'19. orientierte Granatentmischungen in Pyroxenen bei der Rrcrwooo. P. C., M. Mlrstls, nNo J. C. Stersnr (1968)A study metamorphen Genesegranatfiihrender Ultramafitite des Ulten- of garnetsfrom eclogite and peridotite xenoliths found in tales, Stdtirol. Ber. deutsch. ges. geol. lltiss B. Mineral Lager' kimberlite.Contrib. Mineral. Petrol.19, 271-301. stdt t enfo rsch. 16, 227-240. Rosn, F., ANDD. G. BroortNs (1966)The mineralogyof the Brcnowsrt, B. P (1941) Pyrope garnet us ruby spinel in Kansas. Stockdalekimberlite pipe, Riley County, Kansas. Trans. Kansas Am. Mineral. 26, 675-676. Acad.Sci 68.72-87. BRooKINs, D. G. (1967) Re-examination of pyrope from the Rosr, F , nxo H. Hrusnrn (1954) Der Doppelelektroden- Stockdale kimberlite, Riley County, Kansas. Mineral. Mag'36, Wechselstrombogen.Vergleichende Untersuchungen iiber 450-452 Ableuchtungsartenim Kohledauerbogen.Z. angew Phys.6, - (1970) The kimberlites of Riley County, Kansas. Kczs. 275-2'79. Geol. Suru. Bull. 2UJ, l-32. -, ANDW. Gnrcrl (1964)Uber accessorischeElemente in Ensrwoon, R. L., lNo D. G. BnoortNs (1965) A spectrochemical mitteleuropiiischenEklogiten und ihren Mineralien.Geochim. investigation of the Bala and Stockdale Intrusions Riley County, Cosmochim.Acta, 2t, 1933-1951. Kansas. Trans Kansas Acad. Sci 6t, 72'87. -, AND- (1969)Zur Geochemieund Genesegranat GnNoor-rt, G. (1967) Discussion upon methods to obtain X-ray fiihrenderUltramafitite des mitteleuropiiischen Grundgebirges. "powder patterns" from a single cryslal. Mineral. Petrogr. Acta, Chem.Erde. 28, 91-177. 13, 67-'14. -, J. WeNrrltlcHrn, ANDW. GrIcrl (1974)Die Ultramafi- GunNrY, J. J., lNn G. S. Swtrzrn (1973)The discoveryofgarnets tite der Alpe Arami und Croveggio,Tessin (Schweiz). Schweiz. closely related to diamonds in the Finch Pipe, South Africa. Mineral. Petrogr. Mitt. 54, 353-369 Contrib. Mineral. Petrol. 39' 103-116. Sosolrv, N. V., Yu. G. Levnrxr'vnv,L. J. PosPELovl,lwo V. S' Mrvnn, H. O. A (1968)Chrome pyrope: An inclusion in natural Sonolrv (1969)Chrome pyrope in diamondsfrom Yakutia' diamond. Science, 160, 1446-144'1. Dokl Akad. Nau&.SS,SR, lt9' 162-165. - (1970) G6ochimie des inclusions min6rales dans les Dia- WHrrr,W. B., R. Rov, rNo J. Mcr. CntcnroN(1967) The "Alex- mants naturels. Bull. Assoc. Franc. de Gemmol 22 (2 pages). andriteeffect": an optical study.Am. Mineral. 52,867-871. -, AND D. G. Bnoornts (1971) Eclogite xenoliths from WrrLrrtvts,A. F. (1932)The Genesisof the Diamond.London. Stockdale kimberlite, Kansas. Contrib' Mineral. Petrol. 34, 60-72. -! AND F. R. BoYD (19?2) Composition and origin of crystal- August 15, 1974; accepled line inclusions in natural diamonds. Geochim Cosmochim.Acta, Manuscript receiued, FebruarY 21,1975. 36. 1255-1273. for publication,