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Soils, rocks, and groundwater
Published in Rodrigo Salgado, The Engineering of Foundations, Slopes and Retaining Structures, 2022
Rocks originating from magma with the same chemical composition will still differ in appearance and properties depending on the rate of cooling of the magma during rock formation. Extrusive rocks, as we have seen, will be fine-grained, while intrusive rocks will be coarse-grained. In terms of their chemical composition, rocks with large silica content and low iron and magnesium content are called granitic or felsic rocks. As the silica content decreases and the iron and magnesium content increases, rocks are classified as andesitic and then, for even lower silica contents and higher iron and magnesium contents, as basaltic. Table 3.3 provides the main igneous rocks and their most important features.
Igneous Petrology and the Nature of Magmas
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
Petrologists classify and group igneous rocks (and magmas) in many ways, but at a fundamental level, rocks that are relatively rich in silica, such as granite or rhyolite, are termed felsic. Those relatively poor in silica, such as basalt, are mafic. Those that fall between (andesite and syenite) are intermediate. Rare rocks with the lowest silica contents are termed ultramafic. The rocks in Table 5.1 have silica contents ranging from 40.08 (ultramafic rocks) to 77.24 (felsic rocks) wt%. Rocks with silica contents outside this range exist but are rare. Because of the high-silica content in magmas, most minerals in igneous rocks are silicates.
Major, trace and rare earth element geochemistry of the Permian Lucaogou oil shales, eastern Junggar Basin, NW China: implications for weathering, provenance and tectonic setting
Published in Australian Journal of Earth Sciences, 2023
M. Zhao, Y. Liu, X. Jiao, D. Zhou, Z. Meng, Y. Yang
Trace-element (e.g. Sc, Cr, Co, La, Hf and Th) concentrations and/or ratios in clastic sediments are also commonly used to deduce their provenance because these immobile elements are unaffected by diagenesis and metamorphism (Armstrong‐Altrin et al., 2013; Bhatia & Crook, 1986; Liu et al., 2020; Wang et al., 2018). Felsic rocks generally show enrichments in La and Th, whereas Sc, Cr and Co are more abundant in the mafic rocks (Armstrong‐Altrin et al., 2013; Cullers & Berendsen, 1998). The Th/Sc ratios of our samples (J1, 0.36–0.92; J2, 0.32–0.68; S, 0.65–2.65) are much lower than the Zr/Sc ratios (J1, 13.24–21.30; J2, 14.06–24.92; S, 23.77–46.84), and most samples exhibit a positive linear relationship in the Zr/Sc vs Th/Sc diagram (Figure 7e), indicating a felsic origin without sediment recycling. The Co/Th ratios (J1, mean of 1.85; J2, mean of 1.14; S, mean of 1.84) are generally higher than that of UCC (0.9, Taylor & McLennan, 1985). In the La/Sc vs Co/Th diagram (Figure 7f), most samples fall in the andesite and felsic volcanic rock areas. A plot of Hf vs La/Th (Figure 7g) also offers a reliable basis for mixed provenance with most samples plotting in the intermediate and felsic sources.
Predictive quantitative model for assessing the asphalt-aggregate adhesion quality based on aggregate chemistry
Published in Road Materials and Pavement Design, 2021
Within siliceous rocks, the mafic-felsic classification is commonly used. Mafic rocks refer to those with relatively high contents of Mg and Fe (e.g. serpentinite, basalt and gabbro), whereas felsic rocks are those with high contents of quartz and feldspar minerals (e.g. granite, quartzarenite and granodiorite) (Marshak & Repcheck, 2009). It should be noted that since this classification is made for siliceous rocks, both mafic and felsic rocks have silica as their major constituent. For calcareous rocks, several different chemical classifications have been proposed (e.g. Dunham, 1962; Folk, 1980). However, for the pavement engineering field, a simpler classification based on its SiO2 content might be more useful. This is due to the fact that although the SiO2 contents in these rocks are naturally much lower than in the siliceous rocks, they have consistently been found to be the main culprit in the moisture susceptibility of the asphalt-aggregate system (Cala et al., 2019; Kim et al., 2008).