Achondrites and igneous processes on asteroids

The possible roles of partial melting and fractional crystallization in the formation of eucrite and ureilite achondrites are discussed, summarizing the results of recent petrological investigations and theoretical modeling efforts. Typical data are presented graphically, and it is found that there is as yet no consensus on the correct model of achondrite evolution, and hence no agreement on the chemistry of the parent bodies. Assuming that the ureilites formed as adcumulates, their properties support a role for fractionation in relatively small bodies, even though the magmatic composition of the ureilite parent bodies is different from that of terrestrial cumulates.