Weathering of Chondritic Meteorites

Meteorites are frequently not the pristine record of early solar system processes that we would like them to be. Many unique meteorites, samples that can further our understanding of the environment of the early solar system, are finds, so a knowledge of terrestrial weathering becomes a requirement to accurately interpret their preterrestrial history. This chapter outlines the weathering process in chondrites, the mineralogical changes that occur in response to weathering, the variations in weathering in different environments, the effect of weathering on O isotopes and chemistry, and how weathering varies between different chondrite groups. As the most abundant meteorite group, most studies of meteorite weathering have concentrated on ordinary chondrites, although weathering affects all classes of meteorites. In many cases, these data are relevant to other chondrite groups, as well as irons and achondrites, but there are a number of specific issues related to carbonaceous chondrites (degradation of organic C, mobilization of S, reordering of phyllosilicates) that require a separate discussion. In particular, carbonaceous chondrites appear to be uniquely susceptible to terrestrial weathering, and recent studies have shown a number of alteration effects, even in falls curated in museum collections. The terrestrial alteration of carbonaceous chondrites concludes our chapter.