Granitization is an old, and largely discounted, hypothesis that granite is formed in place through extreme metasomatism. Fluids bring in elements, such as potassium, and remove others, such as calcium, to transform a metamorphic rock into a granite. This was supposed to occur across a migrating front. However, experimental work had established by the 1960s that granites were of igneous origin. The mineralogical and chemical features of granite can be explained only by crystal-liquid phase relations, showing that there must have been at least enough melting to mobilize the magma.