At 10:30 in the evening, a highly friable stone meteorite weighing ~330 kg fell on sea-ice in Borga, Finland and broke into many fragments. A subsequent analysis determined a classification of L4 chondrite. Further studies of Bjurböle have resulted in a revision of this classification, now recognized to belong to the L/LL4 transitional group. The extrememly low crushing strength implies a crystallization at low pressures and/or within a small body.
Previous parameters used to delimit the L/LL group from the L and LL groups include the fayalite molar percentage and the content of cobalt 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 negative europium anomaly that are found only in the L/LL meteorites easily distinguishes them from the other groups; the evidence is stronger for the existence of a separate L/LL, low total-Fe, chondritic parent body.
Other members of this newly recognized intermediate chondrite group include the L/LL3 Esperance, the L/LL4 Seemore Downs 001 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 Bjurböle shown above is a 0.2 g micromount with a small detached chondrule.
