Unit 11 Chapter 1- Clay Minerals When we studied soil texture we learned that one of the soil separates was called clay. Now we learn more about this important mineral component of the soil. Clay minerals are the most important chemical weathering product of the soil. They are formed by the alteration of existing minerals or by synthesis from elements when minerals weather to their elemental form. It is not possible to make clays by grinding up silt or sand particles. Clay has many uses today including, pottery , ceramics, linings for landfills, computer chips, cosmetics, and pharmaceuticals. Clay minerals are important in soils because of the negative charge they contribute for cation exchange. nderstanding about soil clays is also important because of their shrink and swell potential upon wetting and drying. When soils are unsuitable for building because of a high shrink!swell potential this is because of the amount and type of clay present. "ur study of clay minerals will involve looking at their structure and why this contributes to their properties. Clay minerals are part of the larger class of silicate minerals# the phyllosilicates. Included in the phyllosilicate family are the larger true micas which include the familiar minerals muscovite and biotite. $uch of what we know about clay minerals is from the macroscopic %i.e., single crystal& study of the true micas. 'ilicate Clay $inerals are called aluminosilicates and they have a definite crystalline structure. Clay minerals are very small in si(e %by definition are less than ).))* mm in si(e& and only seen with aid ofelectron microscope. +uilding +locks for Clay $inerals Clay minerals are composed of two basic building blocks. 1) Silicon - OxygenTetrahedron %'i*"-*& 2)Aluminum Octahedral%ibsite 'heet& /l%"0& 1 -2 Tetrahedral sheets are composed of individual tetrahedrons which share every three out of four oxygens. They are arranged in a hexagonal pattern with the basal oxygens linked and the apical oxygens pointing up!down. "ctahedral sheets are composed of individual octahedrons that share edges composed of oxygen and hydroxyl anion groups with /l, $g, 3e24 and 3e*4 typically serving as the coordinating cation. These octahedrons too, are arranged in a hexagonal pattern and called a gibsite sheet.
