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Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
The rocks comprising El Capitan are typical of the entire Yosemite region and of the Sierra Nevada Mountains overall. Yosemite is a mosaic of many different intrusive bodies that formed over millions of years, including some additional rock types not seen in El Capitan’s face. Figure 6.19 shows a sample of the Half Dome Granodiorite. It crops out just a few kilometers east of El Capitan on the north side of the valley in the Royal Arches and North Dome. The Royal Arches are prominent in Figure 6.5; North Dome is the rounded peak above the Arches. This granodiorite also crops out on the opposite side of the valley from the Arches, at Glacier Point. Farther east, it forms the vertical cliff face of Half Dome itself, seen in Figure 6.5. The granodiorite is medium to coarse grained and contains conspicuous plates of biotite and crystals of hornblende. It is the youngest of the major plutonic rocks in the region. The granite, granodiorite, tonalite, quartz monzonite, and quartz monzodiorite found in Yosemite are all considered granitoids, and this explains why sometimes the imprecise name granite is used for all of them. Other rocks—including quartz diorite, diorite, and gabbro (none of which are granitoids)—are present too, but in lesser amounts and are not called granite.
Igneous Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
Granitic rocks in which the plagioclase content is greater than that of the potash-feldspar are called granodiorites; their dark minerals (biotite, hornblende) are usually rather more plentiful than in granite, and the amount of quartz is less. As shown in Fig. 5.17 (p. 100), granodiorite is transitional between granite and diorite; its texture is normally coarse-grained. The name tonalite (after the Tonali Pass, Italy) is used for similar rocks in which the plagioclase content is more than two-thirds of the total feldspar; and adamellite (after Mt Adamello) for those in which the potash-feldspar and plagioclase are nearly equal in amount.
Natural aggregate sources and production
Published in Mark Alexander, Sidney Mindess, Aggregates in Concrete, 2005
Mark Alexander, Sidney Mindess
Fresh or slightly weathered granites generally make excellent concrete aggregates. Weathering results mainly in the conversion of the feldspars to clay minerals, but these are usually of a stable variety such as kaolinite and/or illite. Occasionally weathering of the mica minerals may cause some dimensional instability in concrete, and weathered granites must be carefully examined and tested before being used in concrete. Granodiorite is a rock similar to granite, except the dominant feldspar is plagioclase.
ASR performance of concrete at external alkali supply – effects of aggregate mixtures and blended cement
Published in International Journal of Pavement Engineering, 2023
Michał A. Glinicki, Karolina Bogusz, Daria Jóźwiak-Niedźwiedzka, Mariusz Dąbrowski
Granodiorite was composed of similar minerals like granites but it contained less quartz and more plagioclase and orthoclase feldspar. It also contained amphibole, mica and biotite. As a reactive form of SiO2 the micro – and cryptocrystalline form was found as well as strained quartz. Quartz occurs in the form of stretched and elongated microcrystals and as micro – and cryptocrystalline form in micro-cracks in the immediate vicinity of larger quartz crystals. Large quartz grains show undulatory extinction.
Has the tectonic regime of the Baltic Shield always remained the same?
Published in GFF, 2022
The Bergslagen unit (Fig. 6) is composite and shows similarities with the Bothnia-Skellefte unit. Volcanic rocks, at places mineralized, metasedimentary rocks and sequences of granitoids are important. The Svecokarelian volcanic rocks are dominated by rhyolite, partly strongly metasomatized, besides significant amounts of basalt; an andesite gap exists. Among the plutonic rocks, granodiorite is frequent.