A basaltic magma with a low magnesium number (Mg#) and low content of MgO (magnesium oxide). Such magma results from crystals separating from a melt in which the liquid in equilibrium with the solid has a lower Mg# than the solid, so as olivine is removed the Mg# falls and since olivine at the forsterite (Mg2SiO4) end of the series is rich in MgO, the level of MgO will fall also.