Diorite is an intrusive rock intermediate in composition between gabbro and granite. It is produced in volcanic arcs, and in mountain building where it can occur in large volumes as batholiths in the roots of mountains (e.g. Scotland, Norway). Because it is commonly speckled black and white, it is often referred to as "salt and pepper" rock. Diorite is the plutonic equivalent of andesite.
Colour - typically speckled black and white.
Texture - phaneritic (medium to coarse grained).
Mineral content - plagioclase, amphibole (hornblende) and / or pyroxene (augite).
Silica (SiO2) content - 52%-63%.
Uses - can be used as aggregate, fill etc. in the construction and roading industries (often not ideal for concrete aggregate because of high silica content); cut and polished for dimension stone for building facings, foyers etc.
New Zealand occurrences - Northland, Coromandel Peninsula, west Nelson area, Fiordland, Stewart Island.