The diversity of chondrules

Chondrules are highly diverse in their properties. They all appear to have been melted to some degree at some point; some are clearly melt droplets that have crystallized; some appear to be igneous systems that have been subsequently rounded. Most are deficient in metal and sulfide in comparison with the host rock, some have additional compositional differences. Some have thick rims of material, some do not, and in some cases those rims are rich in metal and sulfide, and in some cases they are not. The nature of the chondrules, and their diversity, tells us something about conditions in the early Solar System. Chondrules are the major component of chondrites and must account for many of their bulk properties, as does their relative abundance in the various classes of meteorites (Huang et al., 1996b). It also seems clear that accounting for the diversity of properties will provide insights into their formation process.

Attempting to understand objects as diverse as chondrules starts with their classification and there have been many proposed schemes. However, all the schemes have common features and it is possible to trace a development of ideas. In this way I hope to focus on the important observations without getting bogged down in the plethora of detail, much of which may be extraneous. There has been a long-term trend of textural classification schemes giving way to composition-based schemes as analytical instruments improved and trends became clearer.