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The quartz percentage among felsic minerals in TTG rocks is usually larger than 20% but less than 60%. [1] In tonalite and trondhjemite, more than 90% of the feldspars are plagioclase, while in granodiorite, this number is between 65% and 90%. [1] Trondhjemite is a special kind of tonalite, with most of the plagioclase in the rock being ...
Trondhjemite is a leucocratic (light-colored) intrusive igneous rock. It is a variety of tonalite in which the plagioclase is mostly in the form of oligoclase . [ 1 ] Trondhjemites that occur in the oceanic crust or in ophiolites are usually called plagiogranites .
Trondhjemite is an orthoclase-deficient variety of sodium-rich tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim. [6] Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones. [7]
Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and sometimes pyroxene.The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite.
However, the IUGS allows the use of the term to describe rocks close to the boundary between the rhyolite and dacite fields in each classification scheme. Rhyodacite then describes a fine-grained igneous rock containing between 20% and 60% quartz and in which plagioclase makes up about two-thirds of the total feldspar content.
Monzonite is found in association with gabbro and granodiorite in the Khankandi pluton in the Alborz Mountains of Iran. The monzonite likely formed during the collision that closed the Tethys Ocean, from partial melting of upper mantle that had previously been altered by fluids released from a subducting ocean crust slab.
Late-stage charnockite dykes cutting anorthosite, Rogaland, Norway Job Charnock's Mausoleum at St John's Church compound, Kolkata. Charnockite (/ ˈ tʃ ɑːr n ə k aɪ t /) is any orthopyroxene-bearing quartz-feldspar rock formed at high temperature and pressure, commonly found in granulite facies’ metamorphic regions, sensu stricto as an endmember of the charnockite series.
Pietersite is a commercial term for a variety of the mineral chalcedony. Originating from Namibia and China, where it is mined for use as a decorative stone due to its chaotic chatoyancy and brecciated structure. Ranging in colour from brownish-red, to blue-grey, and chatoyant yellow.