Note Practical charts to identify the predominant clay mineral based on oxide composition of clayey soils Osman Sivrikaya a, ⁎, Burak Uzal b , Yunus Emre Ozturk c a Department of Civil Engineering, Niğde University, 51240, Turkey b Department of Civil Engineering, Abdullah Gul University, 38039, Kayseri, Turkey c General Directorate of TEDAS, Balgat, 06490 Ankara, Turkey abstract article info Article history: Received 12 July 2016 Received in revised form 29 September 2016 Accepted 30 September 2016 Available online xxxx This study proposes some useful practical charts representing the relationships between oxide composition and the type of predominant clay mineral present in clay soils. In order to produce the charts, the data set are collected from published literature. Some useful classification schemes for predominant clay mineral type were obtained by using binary and ternary graphs of oxide composition data. The most successful relations indicating the type of clay mineral have been found on SiO 2 versus Al 2 O 3 + Fe 2 O 3 + FeO, SiO 2 versus MgO + CaO + Na 2 O+K 2 O binary plots, SiO 2 - Al 2 O 3 - Others and SiO 2 - Al 2 O 3 - K 2 O ternary plots. © 2016 Elsevier B.V. All rights reserved. Keywords: Geotechnical engineering Soil mechanics Clay minerals Oxide composition Mineral identification 1. Introduction Mineral type is one of the most important properties of fine-grained soils. The colloidal particles of soils are mainly composed of clay min- erals that occur in all type of sediments and sedimentary rocks as a re- sult of weathering and hydrothermal alteration. All the clay minerals are layered crystalline hydrous aluminosilicates, and the arrangement and the chemical composition of the layers determine the type of clay mineral (Holtz and Kovacs, 1981; Craig, 1994; Terzaghi et al., 1996; Weaver and Pollard, 1973). Clays are defined as soils which have particles smaller than 2 μm and cohesive effects. The influence of the electrical forces acting at the sur- face of each particle is significant. It is very complicated and difficult to classify the mineral types. However, various groups exist based on min- eralogical and chemical structures in the literature. In terms of geotech- nical engineering, clay minerals are mainly classified as kaolinite group, micalike minerals group and Smectite group (Lambe and Whitman, 1979; Mitchell, 1993). It is so difficult to find pure clay mineral compos- ing of only one mineral on earth. However, it is possible to estimate be- havior of clays from geotechnical point of view as the predominant mineral existing in clay is known. For geotechnical engineers the mineralogical composition of clays may be useful as a notice of their characteristic behavior, and as an indi- cation of the difference from the other materials (Holtz and Kovacs, 1981). Sizes, shapes and surface characteristics of the clay particles as well as their interactions with fluids are governed by the mineralogy. Therefore, mineralogical characterization is essential for understanding of geotechnical properties of clayey soils such as plasticity, swelling, compression, strength, and permeability. It also gives us good estima- tion about the consistency limits and grain size distribution reflecting both composition and engineering properties (Mitchell, 1993). The consistency limits are very useful for soil identification and classi- fication. In addition, they are widely used as a means of estimating the plastic properties of clay materials. The liquid limit (w L ) and plastic limit (w p ) are in the order montmorillonite N illite N kaolinite for common clay minerals belonging to smectite group, mikelike minerals group and kaolinite group, respectively (Mitchell, 1993; White, 1949; Bain, 1971). Susceptibility of clays to swelling and shrinking increases with increasing activity (A c ). Therefore, the swelling and shrinking potential is in the order montmorillonite N illite N kaolinite for clay minerals. For clay min- erals compared at the same water content, the permeability is in the order montmorillonite b illite b kaolinite. The compressibility of saturated clay minerals decreases in the order montmorillonite N illite N kaolinite (Mitchell, 1993). The angle of shear strength decreases in the order by ka- olinite, illite and montmorillonite for clay minerals (Olson, 1974). One of the most important issues for geotechnical engineers is to esti- mate behavior of clayey soils, which is mainly governed by the dominant clay type. Although identification of mineralogical composition of clay samples by XRD analysis is an easily applicable technique for clay scientist, the specimen preparation and assessment of XRD patterns to determine the available minerals in clay soils is a complicated methodology for Applied Clay Science xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail address: osivrikaya@nigde.edu.tr (O. Sivrikaya). CLAY-04005; No of Pages 6 http://dx.doi.org/10.1016/j.clay.2016.09.035 0169-1317/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Please cite this article as: Sivrikaya, O., et al., Practical charts to identify the predominant clay mineral based on oxide composition of clayey soils, Appl. Clay Sci. (2016), http://dx.doi.org/10.1016/j.clay.2016.09.035