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Geology of Urban Watersheds
Published in Daniel T. Rogers, Urban Watersheds, 2020
There are four basic types of sand deposits (Pettijohn et al. 1987; Boggs 2000): Quartz arenites consist almost entirely of quartz grains, are usually well-sorted and well-rounded. Quartz arenite deposits result from extensive weathering, so they consist of only the most resistant minerals. Figure 2.25 is an example of a quartz arenite sand that is medium grain, well-sorted, with sub- to well-rounded grains.Arkoses are sand deposits with a composition of 25% feldspar or more. The grains tend to be poorly rounded and less well sorted than quartz arenites. Arkoses originate from rapidly eroding granitic and metamorphic rock where physical weathering is dominant.Lithic sand deposits contain many fragments derived from fine-grained materials, mostly shales, volcanic rocks, and fine-grained metamorphic rocks.Greywacke is a heterogeneous mixture of rock fragments and angular grains of quartz and feldspar; the sand grains become surrounded by a fine-grained clay matrix.
Sedimentary rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
Classification Several sandstone classifications have been proposed based on the abundances of the components described above. We give an example of classification using QFR diagrams. These are triangular diagrams with quartz, feldspar and rock fragments at the poles. The main triangle is for arenites, sandstones containing less than 15% fine-grained matrix (Figure 128). The volume of all components is estimated and the quartz, feldspar and rock fragment components recalculated to total 100%. Granite and gneiss fragments, where present, plot with feldspar in this classification rather than with rock fragments. This is because most feldspar derives from weathered granites and gneisses and as far as possible fragments with a common origin should be plotted together. In using this diagram it is best to take the quartz percentage first. Any rock with more than 95% quartz is a quartz arenite. A rock with 75–95% quartz is a sub-arkose if feldspar is more common than rock fragments and a sub-litharenite if rock fragments dominate over feldspar. Rocks with less than 75% quartz are classified according to the ratio of feldspar to rock fragments.
Sedimentary Petrology
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Quartz arenites consist almost entirely of quartz grains cemented together by silica or welded together by predissolved quartz (see diagenesis). Chemical precipitates other than silica may also serve as cement. The quartz grains constituting the framework are often well rounded and well sorted (Fig. 4.4). A small amount of heavy minerals of stable variety (tourmaline, zircon, rutile, ilmenite) may be present in quartz arenites. The Rewa sandstones of the Vindhyan Supergroup may be cited as an Indian example of quartz arenite. Modal analyses of representative samples of Rewa sandstones are presented in Table 4.2.
Mapping a coastal transition in braided systems: an example from the Precipice Sandstone, Surat Basin
Published in Australian Journal of Earth Sciences, 2018
V. Bianchi, F. Zhou, D. Pistellato, M. Martin, S. Boccardo, J. Esterle
The main lithology encountered is very coarse- to medium-grained quartz arenite, fine- to very fine-grained quartz arenite with kaolinite clay matrix, granule to medium-pebble conglomerate and siltstone to mudstone beds. The conglomerates are composed of clasts of slightly metamorphosed siltstone and quartzite from the underlying Triassic strata (Fielding et al., 1996; Ziolkowski et al., 2014) with occasional coal chips. The coarse-grained sandstone is well sorted and mature, has well-rounded grains and is very porous. The finer-grained quartz arenite has a kaolinite clay matrix derived from weathered micas, which supports the development of ‘caves’ and overhangs in outcrops (Wray, 2009; Young & Wray, 2000). From west to east along the outcrop, the expression of the Precipice Sandstone changes, as does the nature of its erosive base.
Archeometric characterization of indigenous LBA/EIA pottery from SW Iberia
Published in Materials and Manufacturing Processes, 2020
Michał Krueger, Violeta Moreno Megías, Dirk Brandherm
The coarse fraction comprises frequent macro and mega inclusions, including common mega rock fragments measuring more than 3 mm in Subgroups A and B. In general, the presence of metamorphic and igneous rock fragments (chloritoid schist/gneiss/diorite) can be interpreted as temper, due to its angular shape (crushed fragments), and different size, shape and distribution from the rest of the matrix. Beside these predominant rock fragments, common inclusions are subangular plagioclase and amphibole. Less frequent components consist of quartz arenite, subrounded polycrystalline quartz, biotite, orthoclase and muscovite (in order of frequency). All these components are also present in the fine fraction (0.10 mm or less).
Determination of the natural radioactivity, elemental composition and geological provenance of sands from Douala in the littoral region of Cameroon using X-ray and γ-ray spectrometry
Published in Applied Earth Science, 2019
Joel Cebastien Shouop Guembou, Maurice Moyo Ndontchueng, Jilbert Eric Mekongtso Nguelem, Gregoire Chene, Ousmanou Motapon, Styve Arnol Kayo, David Strivay
The high ratio of K2O/Na2O is due to the generally regular nearness of K-bearing minerals, for example, K-feldspar and a few micas (McLennan et al. 1983; Nath et al. 2000; Zhang 2004; Osae et al. 2006; Kalsbeek et al. 2008; Anani et al. 2013). The correlation between K2O and Al2O3 shows a positive gradient as seen in Figure 4. This positive correlation of K2O and Al2O3, as shown in Figure 4, suggests that the concentrations of the K-bearing minerals have a noteworthy impact on Al distribution in the investigated sand samples as well as in the study area. Therefore, the relative influence of these components (K2O and Al2O3) is basically controlled by the substance of mud minerals (McLennan et al. 1983; Caridi et al. 2015). Considering the diagram of Herron as shown in Figures 5 and 6, 37.5% of the studied samples were chemically classified as Subarkose (the sample from Northern Akwa AN1 to AN6 and from Youpoue-Bamenda YB2 and YB4 …), 12.5% as Fe-sand (sand from Village V1 and V2, and from Bonaberi Bonamikano BB3), and 25% as Sublitharenite (sand sample from Bonaberi Bonamikano BB1, from Youpoue YO2 and YO3 and from Youpoue-Bamenda YB1 …). These results are further supported by low Al2O3/SiO2 ratios that easily allowed the classification of some other samples; the remaining 25% are classified as quartz arenites (sand from Dibamba D2, from Youpoue-Bamenda YB2 and YB3 and Bois de Singe BS3 and BS4 …) (Pettijohn et al. 1987; Anani et al. 2013; Caridi et al. 2015).