Diorite has a medium grain size texture, occasionally with porphyry. Diorite is very hard, making it difficult to carve and work with. It has been used as structural stones and pavement cobblestones. It has also been used for statuary, and can take a high polish. Diorites may be associated with either granite or gabbro intrusions, into which they may subtly merge. Diorite results from partial melting of a mafic rock above a subduction zone. It is commonly produced in volcanic arcs, and in cordilleran mountain building such as in the Andes Mountains as large batholiths. The extrusive volcanic equivalent rock type is andesite.
Diorites are truly igneous; they have crystallized from molten material. Occassionally, we find others that are products of reactions between magma and included fragments of foreign rock (xenoliths). Many have been chemically transformed (metasomatized) in the solid state from some pre-existing rock, such as gabbro, by the loss of certain constituent atoms and the gain of others.