Bilson (1978) has criticized our interpretation of ion probe measurements on lunar plagioclase grains by contending that the sputter action of solar wind H and He can account for observed surface enhancements of Mg and Fe. We think that an inappropriate analogy between lunar bulk soils and plagioclase grains led Bilson to this conclusion. While it is true that ion implantation is unlikely to have a dominant effect on the major element composition of the surface of lunar grains of average bulk soil composition, we show that chemical alteration by solar wind sputtering cannot explain our ion probe result on plagioclase grains. Glass splashes on shielded grains and solar wind implanted ions on some selected exposed crystals are the most likely source of Mg and Fe enhancements.
Geophysical Research Letters
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