[meteorite-list] AD - Do you want a rareandimportantMetachondrite?

[stan .]

>This is interesting as I've never heard this before. Can terrestrial
>weathering really have a significant effect on oxygen results?

yup - oxygen isotopse analysis basically involves vaporizing a bit of the 
meteorite with a laser in a strongly oxydyzing environment - normally 
flourine. basically all atomic bonds between atoms int he meteorite are 
broken down int he vaporized bit freeing up any of the chemically 
sequestered oxygen. the flourine atmosphere is present to latch on to 
anything that would otherwise want to bond back with the now free oxygen. 
the resulting minute gas sample is sent trought  a series of filters to 
remove these products adn the oxygen then goes to a mass spectrometer to 
identify the ratio between the various isotopse present. any terrestrial 
source of oxygen such as calcium carbonate will therefore alter the ratio of 
the isotopse present.