diorita

Diorita, known in English as diorite, is a coarse-grained, intrusive igneous rock of intermediate composition. It is chiefly composed of plagioclase feldspar with lesser amounts of dark minerals such as hornblende or pyroxene; quartz is typically sparse or absent. The typical color is a salt-and-pepper mix of light crystals against darker ferromagnesian minerals.

Diorite is phaneritic, with crystals large enough to be seen without a magnifying glass. It forms as magma cools slowly underground, giving it a visibly crystalline texture. Its mineralogy distinguishes it from felsic rocks like granite (which contain more quartz) and from more mafic rocks (which contain more dark minerals). The rock is the intrusive equivalent of andesite; its surface counterpart formed by eruption is the andesite lava.

Formation and setting: Diorite crystallizes from silica-rich, intermediate magmas in crustal magma chambers, often in convergent plate-margin environments where subduction generates andesitic magmas. Through crystallization and fractional differentiation, melts can evolve toward dioritic compositions, producing large igneous bodies within the crust.

Occurrence and uses: Diorite occurs worldwide in plutonic complexes and crustal blocks. It is a durable rock often quarried as a dimension stone and used in architectural applications and sculpture. In quarry literature it is sometimes described by its typical “salt-and-pepper” appearance, reflecting the contrast between light plagioclase crystals and dark ferromagnesian minerals.