When found in Western Australia, this meteorite was composed of several large fragments and four smaller pieces having a combined weight of 429 g. Seemore Downs may be a chemically extreme member of the L or LL ordinary chondrite groups, or it may be derived from its own unique parent body with properties intermediate to, or overlapping with, both the L and the LL parent bodies.
Previous parameters used to delimit an L/LL group from the L and LL groups include the siderophile element concentrations, the fayalite content in olivine, and the cobalt concentration in kamacite. New studies utilizing cluster anaysis statistics on the minor and trace element data conclude that the L/LL meteorites are chemically more closely related to each other than they are to either the L or LL group. Furthermore, the enriched REE concentration and the negative europium anomaly, which are found only in the L/LL meteorites, easily distinguishes them from the other groups (Friedrich and Lipschutz, 2001). Moreover, it was ascertained by Heck et al. (2009) that the O-isotopic compositions and the major and minor elemental compositions overlap between the L and LL chondrite groups. Since these meteorites do not fit into either of these two groups, they provide evidence for the existence of a separate L/LL, low total-Fe, chondritic parent body. The gas-retention age distribution determined for a set of 12 L/LL chondrites by Wasson and Wang (1991) revealed a different age range for each L, LL, and L/LL group. This suggests that meteorites from these chondrite groups originated from at least three separate parent bodies. At the close of 2009, the Meteoritical Bulletin Database has listed 102 meteorites classified as members of the L/LL group, although a portion of these may reflect an inability of the classifier to adequately distinguish between the L and LL groups.
Other members of this newly recognized intermediate chondrite group include the L/LL3 Esperance, the L/LL4 Bjurböle and Cynthiana, the L/LL5/6 Sahara 97021, the L/LL6 Acfer 041, and several others. A few meteorites are only partially resolved into the L/LL group including the L/LL3 Inman, the L/LL5 Knyahinya and Qidong, and the L/LL6 Holbrook and Sultanpur. The specimen of Seemore Downs 001 shown above is an 8.9 g partially crusted fragment.
