GranodioriteGranodiorite is an intrusive rock, intermediate in composition between diorite and granite. Although often similar in appearance to diorite or granite, it has a higher quartz content than diorite, and a higher mafic mineral content than granite. It is commonly produced in volcanic arcs, and in mountain building where it emplaces as large batholiths in mountain roots. Granodiorite is the plutonic equivalent of dacite.
Other specimens - Click the thumbnails to enlarge
Colour - variable but typically light-coloured.
Texture - phaneritic (medium to coarse grained).
Mineral content - quartz, plagioclase, with lesser orthoclase, biotite (these separate it from diorite) and amphibole ( hornblende) (plagioclase always greater than 2/3 of total feldspar).
Silica (SiO 2) content - 63%-69%.
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 - minor occurrences in Northland and the Coromandel Peninsula, west Nelson area, Westland, Fiordland, Stewart Island.