Submillimeter grain-size distribution of Apollo 11 soil 10084

Soil 10084 is the only representative soil sample from Apollo 11 and arguab ly one of the purest mare soils in the Apollo collection. It was wet sieved in 1970 and dry sieved in 1971 with different results. Therefore, some dou bt about its grain-size distribution persists. We consider allocation inhom ogeneity, if any, to be a minor cause for the discrepancy. Rather, the diff erence in methodology is likely to be the major cause for different results . We report the results of a new analysis of an allocation of 0.99 g using the contemporary method of wet sieving at Johnson Space Center; this method uses water instead of freon. Our results show that the mean grain size and sorting of the submillimeter fraction of soil 10084 are 4.28 phi (= 51 mum ) and 2.23 phi (= 213 mum), respectively. A significant proportion (14.2%) of the soil is in the <10 <mu>m size range, which contrasts to previous det erminations of 6.4% and 9.8%, respectively. The newly determined grain-size distribution is skewed towards the finest grain sizes. This result is more compatible with the high maturity of this soil than the results of previou s determinations.