Granodiorite

Granodiorite (pronounced /ˌɡrænɵˈdaɪ.ɵraɪt/ or /ˌɡreɪnɵˈdaɪ.ɵraɪt/) is an intrusive igneous rock similar to granite, but containing more plagioclase than potassium 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.

Contents 1 Geology 2 History 3 Etymology 4 References

[edit] Geology

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.

[edit] History

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

[edit] Etymology

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

[edit] References

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

• Media related to Granodiorite at Wikimedia Commons

v · d · eIgneous rocks by composition Type Ultramafic < 45% SiO2 Mafic < 52% SiO2 Intermediate 52–63% SiO2 Intermediate-Felsic 63–69% SiO2 Felsic >69 % SiO2 Volcanic rocks: Subvolcanic rocks: Plutonic rocks: Komatiite Kimberlite, Lamproite Peridotite Basalt Diabase (Dolerite) Gabbro Andesite Diorite Dacite Granodiorite Rhyolite Aplite—Pegmatite Granite

This article related to petrology is a stub. You can help Wikipedia by expanding it.v · d · e