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Definition: granodiorite from Collins English Dictionary

n

1 a coarse-grained acid igneous rock containing almost twice as much plagioclase as orthoclase: intermediate in composition between granite and diorite

[C19: from grano + diorite]


Summary Article: Granodiorite
from Rock and Gem

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.

  • Properties
  • 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

Thin section

Clearly visible in this section, from Strontian, Scotland, are oligoclase, quartz, orthoclase, biotite hornblende, and titanite.

Industrial uses

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”.

Cutting stone

When used as road ballast, granodiorite is often chipped into shape.

© 2008 Dorling Kindersley Limited

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