Granodiorite

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A sample of granodiorite rock from Slovakia

Photomicrograph of thin section of granodiorite from Slovakia (in crossed polarised light)

Granodiorite (pronounced /ˌɡrænɵˈdaɪ.ɵraɪt/ or /ˌɡreɪnɵˈdaɪ.ɵraɪt/) is an intrusive igneous rock similar to granite, but contains more plagioclase than potassium feldspar. It usually contains abundant biotite mica and hornblende, giving it a darker appearance than true granite. Mica may be present in well-formed hexagonal crystals, and hornblende may appear as needle-like crystals.

On average the upper continental crust has the same composition as granodiorite.

Granodiorite is a plutonic igneous rock, formed by an intrusion of quartz-rich magma, which cools in batholiths or stocks below the Earth's surface. It is usually only exposed at the surface after erosion and uplift have occurred.

The Rosetta Stone was carved out of granodiorite, and Plymouth Rock was a glacial erratic of this kind.

External links and references

This article incorporates public domain material from the United States Geological Survey document "Granodiorite definition".

Media related to Granodiorite at Wikimedia Commons

Igneous rocks by composition

Type	Ultra-mafic < 45% SiO₂	Mafic < 52% SiO₂	Intermediate 52-63% SiO₂	Intermediate-Felsic 63-69% SiO₂	Felsic >69 % SiO₂

Volcanic rocks: Hypabyssal: Plutonic rocks:	Komatiite Kimberlite, Lamproite Peridotite	Basalt Diabase (Dolerite) Gabbro	Andesite Diorite	Dacite Granodiorite	Rhyolite Aplite—Pegmatite Granite

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