Granodiorite

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A sample of granodiorite from Massif Central, France
Photomicrograph of thin section of granodiorite from Slovakia (in crossed polarised light)

Granodiorite (/ˌɡrænɵˈd.ɵrt/ or /ˌɡrnɵˈd.ɵrt/) is an intrusive igneous rock similar to granite, but containing more plagioclase than orthoclase-type feldspar. Officially, it is defined as a phaneritic igneous rock with greater than 20% quartz by volume where at least 65% of the feldspar is plagioclase. 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.

Geology[edit]

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

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

History[edit]

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

Etymology[edit]

The name comes from two related rocks: granite and diorite. The grano- root comes from the Latin for 'grain', an English language cognate.

Uses[edit]

Granodiorite is most often used as crushed stone for road building. However, it is also used as ornamental stone.[1]

See also[edit]

References[edit]

External links[edit]

Media related to Granodiorite at Wikimedia Commons