Final answer:
Partial melting of a rock produces a melt that is more felsic than the original composition due to the melting of minerals with lower melting points first, leaving a more mafic residual rock.
Step-by-step explanation:
Partial melting of a rock produces a melt that is more felsic than the original composition of the rock. During the melting process, minerals with a lower melting point, such as quartz and feldspar, which are typically more felsic, melt first. The residual rock, therefore, becomes progressively more mafic as the felsic components are depleted. This difference in composition can be attributed to the original composition of the molten material from which the rock was derived and the cooling process of the molten material that formed the rock. Rocks may be classified based on their mineral content as mafic, felsic, intermediate, or ultramafic, and also on their texture as intrusive or extrusive, which provides clues about their formation environment.