Clay Mineral Group

The Clay Minerals are a part of a general but important group within the phyllosilicates that contain large percentages of water trapped between their silicate sheets. Most clays are chemically and structurally analogous to other phyllosilicates but contain varying amounts of water and allow more substitution of their cations. There are many important uses and considerations of clay minerals. They are used in manufacturing, drilling, construction and paper production. They have geat importance to crop production as clays are a significant component of soils.


Clay minerals are divided into four major groups. These are the important clay mineral groups: 2 groups will be discussed here

The Kaolinite Group

This group has three members (kaolinite, dickite and nacrite) and a formula of Al2Si2O5(OH)4. The different minerals are polymorphs, meaning that they have the same chemistry but different structures (polymorph = many forms). The general structure of the kaolinite group is composed of silicate sheets (Si2O5) bonded to aluminum oxide/hydroxide layers (Al2(OH)4) called gibbsite layers. The silicate and gibbsite layers are tightly bonded together with only weak bonding existing between the s-g paired layers.Uses: In ceramics, as a filler for paint, rubber and plastics and the largest use is in the paper industry that uses kaolinite to produce a glossy paper such as is used in most magazines.

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The Montmorillonite/Smectite Group

This group is composed of several minerals including pyrophyllite, talc, vermiculite, sauconite, saponite, nontronite and montmorillonite They differ mostly in chemical content. The general formula is (Ca, Na, H)(Al, Mg, Fe, Zn)2(Si, Al)4O10(OH)2 - xH2O, where x represents the variable amount of water that members of this group could contain. Talc's formula, for example, is Mg3Si4O10(OH)2. The gibbsite layers of the kaolinite group can be replaced in this group by a similar layer that is analogous to the oxide brucite, (Mg2(OH)4). The structure of this group is composed of silicate layers sandwiching a gibbsite (or brucite) layer in between, in an s-g-s stacking sequence. The variable amounts of water molecules would lie between the s-g-s sandwiches.Uses: Are many and include a facial powder (talc), filler for paints and rubbers, an electrical, heat and acid resistant porcelain, in drilling muds and as a plasticizer in molding sands and other materials.