Luna 24 ferrobasalt as a low-Mg primary melt

The fractional crystallization model for the petrogenesis of the Luna-24 very-low-titanium ferrobasalt is critically evaluated. Arguments are presented that show there is no real evidence favoring either surface of shallow subsurface differentiation of an Mg-rich primary magma; instead there is ample evidence suggesting such is not the case. It is therefore concluded that surface or near-surface fractionation of olivine from a primary vitrophyre/green glass magma did not produce the ferrobasalt composition. The ferrobasalt did not exist as a residual liquid within a differentiated flow, but rather was extruded as a melt in its own right.