Bitteschön:
BISCHOFF A. et al. (1997) Hammadah Al Hamra 180: A unique unequilibrated chondrite
with affinity to LL-group ordinary chondrites (Meteoritics 32-4, 1997, A014):
Summary: The large range of O isotopic compositions indicates the unequilibrated nature of HH 180. Similar O compositions are known from enstatite chondrites [5], but considering the mineralogy (abundant olivine, Fe-rich pyroxene), a relationship to meteorites of the enstatite chondrite group can be ruled out. The O isotopic compositions follow a roughly linear trend, slightly above the terrestrial fractionation line. Only one analysis (clast 4) falls near the field of LL3 chondrites [6]. All other data have lower values of D17O, which might be the result of extensive terrestrial weathering. However, weathering effects of this magnitude have not been observed in any chondritic "finds" [6]. If the high d18O compositions are not due to weathering, then HH 180 represents a new type of chondritic material. Except for the large inclusions, HH 180 exhibits petrographic features such as chondrule size and texture, indicating some affinity to highly unequilibrated LL-group chondrites. This affinity is supported by mineral and bulk-rock compositions.
TABLE 1. Oxygen isotopes:
d18O d17OWhole rock, untreated 8.14 5.07
Whole rock, HCl washed 7.07 4.40
Clast 1, light 4.48 2.10
Clast 1, dark 6.60 3.83
Clast 2 6.48 3.48
Clast 3 7.71 4.78
Clast 4 6.15 4.14
Viel Spaß beim Studieren und Vergleichen!
Bernd
