GRANODIORITE IS AMONG the most abundant of intrusive igneous rocks. A medium- to coarse-grained rock similar to granite, it has more plagioclase feldspar than orthoclase feldspar. Granodiorite can be pink or white with a grain size and texture similar to granite, but the plagioclase generally makes it appear darker, and the hornblende and biotite that are often present give it a speckled appearance. Twinned plagioclase crystals are sometimes wholly encased by orthoclase. Its quartz can be gray to white.
- Rock type Felsic, plutonic, igneous
- Major minerals Plagioclase, K-feldspar, quartz, mica
- Minor minerals Hornblende, augite
- Color Gray, white, or pink
- Texture Medium to coarse
Granodiorite is hard and durable, and is quarried, cut, and crushed for use as road ballast and kerbstones. In the past, it has been used for cobblestones. In modern times, it is also sawn and polished to create flooring, facing for buildings, and worktops, due to its toughness and often attractive speckling. It is one of the stones sold as “black granite”.
When used as road ballast, granodiorite is often chipped into shape.
n 1 a dark coarse-grained igneous plutonic rock consisting of plagioclase feldspar and ferromagnesian minerals such as hornblende [C19: from French
1. a mineral of the plagioclase feldspar group, calcium aluminium silicate, CaAl2Si2O8, occurring in basic igneous rocks; indianite. Plural: anor
1. a very common mineral of the plagioclase feldspar group, sodium aluminium silicate, NaAlSi3O8, usually white, occurring in many igneous rocks.