The uniformity of concentration of lithophile elements in chondrites—with particular reference to Cs

The paper is in two parts. In the first, the dispersion of concentration of the lithophile elements Li, Na, K, Rb, Mg, Ca, Sr, Ba, Al, Sc, Eu, Si, Ti, Zr, Th and U is examined in chondrites. Where twenty or more analyses have been made, relative deviations have been calculated; these range from 5 to 29 per cent. Some of the variation is clearly due to analytical error and it is concluded that the relative deviations of most, perhaps all, lithophile elements is near the lower limit (5 per cent) of the above range. Such small dispersion of concentration for a wide variety of elements, including Li, K and Mg which are sensitive to fractionation, indicates that chondrites have come from a source with an exceptionally uniform composition. It is concluded further that variation of concentration of a lithophile element in the silicate phase, as distinct from the meteorite as a whole, may be even smaller and that the ratio of one lithophile element to the other lithophile elements may turn out to be extremely small indeed. Analytical data of a very high order of excellence (relative deviation of 1–2 per cent) for all elements are evidently required to estimate such small variations precisely.

The second part of the paper is concerned specifically with caesium. This element has been estimated spectrochemically in K—Rb—Cs fractions obtained by ion exchange techniques from six chondrites and seven specimens of basic rock. In the chondrites, the Cs content (ave. 0.12 p.p.m.) and the K/Cs ratio (ave. 7000) remains constant to within the precision of the method of analysis. The magnitude of the average agrees with that (0.09 p.p.m.) of , and but the small variation of the Cs concentration and of the K/Cs ratio contrasts with their observations as they report large variations (× 30 or more). The K/Cs ratio in the seven basic rocks is fairly uniform (in contrast with granites) and similar in general magnitude to that in the chondrites.