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Meteorite Research

Chemical Studies of Chondrites

Chondrites are stony meteorites containing chondrules (spheroidal granules of olivine and/or enstatite or bronzite) embedded in a fine-grained matrix of pyroxene, olivine, and nickel-iron with or without glass. They constitute more than 80% of meteorite falls. (AGI Dictionary of Geological Terms, 3rd ed., 1984)

USGS research seeks to characterize events that changed the composition of meteoritic chondrules after they solidified. Research is concentrated in three areas:

• Disentangling the effects of three, naturally occurring processes on meteoritic chondrules:
• the primary igneous processes that led to the formation of chondrules (this includes initial chemical variation within a chondrule, or mesostasis, which is the result of the initial cooling process);
• chemical replacement (metasomatism) that occurred while the chondrules were still in the parent-bodies and solar nebula; and
• thermal metamorphism (alteration from heat).
• Studying glassy inclusions trapped in olivine in chondrules. These inclusions may retain the compositions of the original igneous melt. The compositions of the inclusions seem to reflect a lower-volatile, perhaps pre-metasomatism, bulk composition for chondrules than do the chemical compositions of the surrounding minerals in the chondrules.
• Characterizing fine-grained chondrules that have lost mesostasis components from their outer regions. This may be the result of aqueous leaching on the parent body.

The magnitude and causes of these processes have wide implications for many aspects of chondrule and chondrite research, as well as interpretations drawn about the early solar system. Understanding the formation processes of chondrite meteorites and the chondrules within them adds to our knowledge of the environment in the solar nebula and on early asteroidal bodies. The results of this understanding will allow us to identify and study any material that may survive from the earliest epochs of the high-temperature processing (chondrule formation) in the solar system.

Announcements of New Meteorites

Announcements of new meteorites are published by the Meteoritical Society, an international organization devoted to the study of extraterrestrial material. The Society oversees the naming of newly found or fallen meteorites and announces them in The Meteoritical Bulletin, which is published in the Society's journal, Meteoritics and Planetary Science. The Editor of The Meteoritical Bulletin is J. N. Grossman, U.S. Geological Survey.

For information about how to get new meteorites named and announced, and for access to archives of past announcements, see the home page of The Meteoritical Bulletin

This work is funded by NASA's Cosmochemistry Program, through a grant to Jeffrey Grossman. Go to http://www.higp.hawaii.edu/ccp/ to learn about this program.