Surface enhancements of iron and magnesium in crystals from lunar rock and soil samples have been measured by ion microprobes and were attributed to solar wind implantation of these elements. In this paper it is shown that these surface enhancements and in particular the Fe/Mg surface concentration ratios can also be explained as resulting from the sputter action of solar wind protons and He ions. Furthermore, since these ions are ten thousand times more abundant in the solar wind than ions of the elements which principally constitute the lunar grains, calculations demonstrate that sputtering by protons and He ions moves approximately a hundred times more Mg atoms, for example, than the number of solar wind Mg ions striking the surface. Ion implantation is unlikely, thus, to have a dominant effect on the major element composition of the surface of lunar grains.