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What Are Clay Minerals?

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  • Written By: Helen Akers
  • Edited By: Jessica Seminara
  • Last Modified Date: 31 March 2014
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    Conjecture Corporation
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Clay minerals are found in several different types of soil. They are considered to be a part of the phyllosilicates family. There are four distinct categories of clay minerals. These categories include kaolinites, illites, smectites and vermiculites.

Soil clay minerals can take on a sandy appearance and feel. One of the properties of clay minerals, silicate, is present in most beach sand. It gives the sand its granular and smooth softness. The color of most silicate like soil tends to be light brown, grayish or white, with some silicates taking on a pinkish hue.

Phyllosilicates tend to contain a large amount of water. This is one of the reasons why beach sand begins to feel moist and cool when it is dug into. The water is actually contained within the silicate sheets that make up the clay's structure.

Some of the structural characteristics of clay minerals include the ability to retain or release water, transform into plastic, expand and form crystals. A clay mineral is usually not isolated in the natural environment. It will typically be mixed with some other form of clay or crystal, such as formica or quartz.

Depending upon their exact mixtures, clay minerals may fall into one of four major classifications. One of those groups is called kaolinites. These minerals are comprised of silicate and aluminum oxide or hydroxide. They are usually used in printing papers, plastics and paints as a filler.

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A second group of minerals is called illites. Silicate and potassium come together in a unique composition to form illites. Clay minerals that fall into this group tend to be used as fillers.

Smectites are a group that consists of layers of silicates and gibbsites. Some of the more well known minerals in this group include talc and saponite. They are used as fillers, in personal hygiene powders and in porcelain.

The largest family of clay minerals is vermiculites, or chlorites. Many of the minerals in this group are not commonly known by name. Silicate is usually combined with iron, aluminum, magnesium or zinc. This group of minerals is usually not used to make commercial materials.

The clays are also categorized according to two different ratios. Minerals can be classified as having a one to one ratio or a two to one ratio. These ratios refer to the types of silicate layers that exist in the mineral's structure, which are called tetrahedral and octahedral. A one to one ratio indicates the structure is made up of one of each type of layer, while a two to one ratio indicates only one octahedral and two tetrahedral layers.

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