A study of large scale chemical variations in the Allende meteorite



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The Allende, Mexico C3(V) is the largest stony meteorite fall recorded. Nine samples of six pieces of the meteorite were analyzed spectrochemically for large scale chemical variations. Nine elements from four geochemical divisions were used in the analyses. Three slabs oriented to obtain the most representative portions were wire sawed from each sample. The slabs were crushed and screened through a 60 [mu] sieve. The homogenized slab material was then split into four splits for each slab. The 108 splits were numbered randomly and analyzed in random order. An optical emission spectrographic analysis method using a demountable hollow cathode source was developed. The method has reduced matrix effects and uses less sample than previous optical emission spectrographic methods. A method for making background correction on a single spectrum when measuring the spectrographic plates on a densitometer was developed. The method requires a minimum of half the transmission readings of previous methods and allows many more samples to be exposed on a single spectrographic plate. The data were evaluated statistically by several methods and the analysis indicates that the Allende meteorite is a well-indurated polymict breccia. The samples show less chemical variation than the slabs. The accuracy and precision of the results compare well with the data reported for the reference Allende bulk samples prepared by the Smithsonian Institution.