A sample of granodiorite from Massif Central, FranceQAPF diagram for classification of plutonic rocksMineral assemblage of igneous rocksPhotomicrograph of thin section of granodiorite from Slovakia (in crossed polarised light)
The term banatite is sometimes used informally for various rocks ranging from granite to diorite, including granodiorite.
Composition
According to the QAPF diagram, granodiorite has a greater than 20% quartz by volume, and between 65% and 90% of the feldspar is plagioclase. A greater amount of plagioclase would designate the rock as tonalite.
Granodiorite is felsic to intermediate in composition. It is the intrusive igneous equivalent of the extrusive igneous dacite. It contains a large amount of sodium (Na) and calcium (Ca) rich plagioclase, potassium feldspar, quartz, and minor amounts of muscovitemica as the lighter colored mineral components. Biotite and amphiboles often in the form of hornblende are more abundant in granodiorite than in granite, giving it a more distinct two-toned or overall darker appearance. Mica may be present in well-formed hexagonal crystals, and hornblende may appear as needle-like crystals. Minor amounts of oxide minerals such as magnetite, ilmenite, and ulvöspinel, as well as some sulfide minerals may also be present.
Geology
Granodiorite near the Roses Lighthouse, Catalonia, Spain.[3][4]
On average, the upper continental crust has the same composition as granodiorite.
Granodiorite is a plutonic igneous rock, formed by 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.
Etymology
The name comes from two related rocks to which granodiorite is an intermediate: granite and diorite. The gran- root comes from the Latingrānum for "grain", an English language derivative. Diorite is named after the contrasting colors of the rock.
The extent of Egyptian granodiorite masonry is unclear. Egypt's 6000-year history makes determining the period of usage difficult as well. Perhaps like porphyry, it was ignored by the successive dynasties of Egypt and only heavily mined during Ptolemaic or Roman times. This is evidenced by the fact that most examples of granodiorite sculpture seem to have come from later dates. However, its presence in the Rosetta Stone implies that they had considerable experience with it and the fact that only newer artifacts are found may simply be because earlier pieces were lost.
Ireland
Granodiorite is quarried in the Newry area of County Armagh with the common name of 'Newry granite'.[7]
Uses
Granodiorite is most often used as crushed stone for road building. It is also used as construction material, building facade, and paving, and as an ornamental stone.[8] The Rosetta Stone is a stele made from granodiorite.[9] The portico columns of the Pantheon in Rome are formed from single shafts of granodiorite, each 12 metres tall by 1.5 metres in diameter.[citation needed]
^These rocks crystallized in depth from magma 300 million years ago. The original magma became deformed during cooling. Once the magma solidified, cracks opened in the rocks and were filled with residual magma, forming light-coloured dykes. Finally, as the magma cooled further, some of the dykes were themselves fractured in shear zones. See: Site of Geological Interest Roses Lighthouse (in Catalan, with a summary in English).
