Diorite (Gr. diorizein, to distinguish) is characterized by its speckled black and white color with occasional shades of dark green or pink. The sizes of grains are coarse and may be pegmatitic. Texture is equigranular or porphyritic. Sometimes diorites are foliated due to the roughly parallel arrangement of the minerals. This igneous rock which measures 18.2 cm. in length, 11.25 cm. in width and 10.35 cm in thickness.
Diorite consists essentially of the mineral plagioclase. One or more of the ferromagnesian minerals like biotite, hornblende and augite may occur.
Diorite is the plutonic equivalent of the volcanic andesite. This rock is rather an uncommon rock, rarely forming large independent mass. It is deposited as stock, boss and dike.
In the Philippines, diorite is one of the important host rocks of some valuable ore deposits like gold, silver and copper. It came from Bo. Tagbac Antipolo, Rizal. It has an accession no. NMR-1144 and was acquired by the National Museum as a donation from MMIC-Antipolo Site. Other places where you can find diorites are Palawan, Bulacan, Cebu, Surigao del Norte, Rizal, Nueva Vizcaya, Zamboanga City, Bohol, Agusan del Norte, Marinduque, Camarines Norte.