MINERALOGICAL NOTES 28r BIr,ruenot, H. W. (1969) Synthesis of lead pyrosilicate and other barysiliteJike compounds. Amer. Mineral. 54, 510-b?l. Bonnoeux,D., aNo J. Le.rznnowrcz(1969) Synthbsede la barysilite pb"SLOr.Bull. Soc. F ranc. M iner aI. C ristallb gr. 92, gg3-3gb. Gr,essnn,F. p. (1964) New data on barysilite. Amer. Mitwra;J.49, 14gfF14gg. ho, J., exn C. FnoNnnr,(1967) Synthesesof lead silicates: Larsenite, barysilite and related phases.Amer. Mineral. 52, l0ZZ-IOg4. Lttznnowrcz, J. (1966) Etude par diffraction des rayons X et absorption infrarouge de la ba.rysilite, MnPb".3Si,Oz, et de compos6s isomorphes. .Acla C ry stal\ogr. 20, 357-363. Pnrrnn, W., eNn A. B. Eenxrr (1g71)Der Strukturtyp desBarysilit, Xyr(pb,Si,Or)*. F or tschr. M ineral. 49, Bg-40. Pnmnn, W., A. B. ElenNrr., axo U. Knppr,pn (1971) Die Kristallstruktur von BleiBarysilit, Pb"Si,O?.Z . Kris tallo gr. 133,44E4EB. SrraxNow, R. D., er.rl C. T. Pnnwrrr (lg6g) Effective ionic radii in oxides and fluorides.Acta Crgstallogr. BZ5, 925-946. Amcrican Mineralogi,st Vol 57, pp 281-283 (1972) SAMPLEPREPARATION FORX-RAY FLUORESCENCE ANALYSIS:LI-BORATEGLASSDISKS Wrr,r,reuLooorNoANDDoucLAsW. Rrrsrr, Rutgers Oniuersity, DepartmentoJGeology Inrnonitcrron X-ray fluorescence analysisis a widely acceptedtechniquefor obtaining rapid chemicalanalysesof geologicsamples.problems have arisen,however,in samplepreparationthat is fast, reproducibleand inexpensive,and which producesa durable, long-lived standard or sample. claisse (1956) pioneerdthe flux-fusion technique for preparation of X-ray fluorescencesamples.Subsequentmodifications by Rose, Adler, and Flanagan (1g62) have been widely adopted. However, fluorescence samplespreparedby briquetting crushedgrassboulesare susceptibleto contamination,are subjectto deterioration,and require finely-machineddies and a laboratory press.A fusedglassdisk sample preparationhas been describedby Norrish and Hutton (lg6g), but the writers experienceddifficulty preparing disks that did not crack upon remoyal from the graphite mold. The writers' proposedtechnique is similar to that developedby stephenson(1969), but eliminates the oven annealing processdesignedto relieve stress within MINERALOGICAL 282 NOTES the glassdisk sample.we also reducedthe LiBoz-to-sampleratio to approachthe eutectic compositionin the system LiOz-BzOg-SiOz' PnPPenertoN Se,rupr,n For major elementanalysisin silicate rocks a lithium- metaborate flux is preparedin the foliowing proportions,and thoroughly mixed: LiBO, 87.00 LarOa 12.20 LiNOs 0.80 100.00 wt Percent Rock samplesare finely ground and mixed with the lithium metaborate flux as follows: 3'000 g FIux Powderedrock samPle 0'450 g' For Na and Mg analysis LiBOz rlisks are fused without heavy absorber.Here we use a sample-to-LiBOz ratio of 1:1' the glassdiskas it cools.SeeFigure 1' a flat An aluminum quenching plunger should be prepared with grams' 200 of weight approxinlate bottom, an OD of 27 mm and' Aflux-samplemixtureisplacedinagraphitecrucible'andfusedi /l\ r I /t\ ON @@ I ,1, -ln_ p--6Omm-->p-7Omm 50mm----->{ plunger' Fig. 1. Dimensional view of graphite crucible and MINERALOGICALNOTES 2{]3 an oven at 1,000"Cfor 4 minutes.'Whenremovedfrom the oven,the crucibleand molten sampleshould be swirled onceor twice to ensure homogeneityand set on a horizontal surface to cool. While bright cherry-red,the molten sampleis lightly quenchedwith the aluminum plunger until the boule retains the form of a flat-topped glass disk. Quenchingtime shouldbe minimizedto enhanceannealingof the glass disk. When thoroughlycool,the crucibleis inverted and tappedlightly to freethe disk. The glassdisk may be embeddedin plastic by placing it facedown in a metal ring mold and filling the mold with castingresin (comparable to "Cadco Casting Resin," Cadillac Plastic & Chemical Co., Detroit, Michigan). When cured, the disk is ground until the full diameterof the glassdisk sampleis exposed. The exposedglassis then readily polishedto give an optimum surfacefor irradiation. Glass disks preparedin this manner are tough and homogeneous. Electronmicroprobescansacrossglasssurfacesshowedno appreciable variations in composition.Samplesembeddedin plastic are nearly indestmctible.Surfacesfor irradiation may be quickly and reproducibly preparedon all samples.Unlike boric acid pelleLs,glassdisks apparently do not deteriorate with time; after six months of constant use, X-ray fluorescencestandards made with USGS Standards II consistently generate reproducible calibration curves of exceptional fit. If contaminated,glass disk samplesmay readily be restoredby polishingaway any contaminatedsurface. With 8 or 10 crucibles,any number of sampledisks may be rapidly preparedin assembly-linemanner. RnrpnoNcns Cr,erssn,F. (1956) Accurate X-ray fluorescenceanalysis without internal btandard. QuebecDept. Mines Preli,m.nep.927. Nonusrr, K. exo J. T. Hurrox (1963) An accurate X-ray spectographic method for the analysis of a wide range of geological samples. Geoch.hn.Cosmoch'im. 4cta,33,431453. Rosn, I[. J., f. Anr,en eNl F. J. Fr,er'recew (1g62) Use of LazOe as a heavy absorber in X-ray fluorescenceanalysis of silisate rocks. U.8. Geol. 9uru., Prof . Pap. 45v8,80-82. Srorrrnrsow, D. A. (1969) An improved flux-fusion technique for X-ray emission analysis.Arnl. Chem.41, 966-967.