The partial or incomplete melting of a rock in response to an increase in temperature (at constant pressure), or a drop in pressure (at constant temperature). Melting takes place along grain boundaries, and the melt can either be extracted from the partially molten rock system, or can remain within the system. Typical examples of anatexis would be the generation of granitic melts (see granite) by partially melting aluminous crustal rocks, and the generation of basalts by partially melting mantle peridotite.