Phyllosilicate

The phyllosilicates , also called lamellate silicates , are mineral of the family of the Silicate S built by stacking of tetrahedral layers (“T”) where the tetrahedrons share three tops out of four (“basal” oxygens), the fourth top (“apical” oxygen) being connected to an octahedral layer (“O”) occupied by different Cation S (Al, Mg, Fe, Ti, Li, etc). The union of the layers T and the layers O forms layers, which represent the unit of cleavage of the phyllosilicates.

In the layer T, the Aluminum can replace the Silicium, in which case the negative charge of the grouping is higher; example the Mica S.

According to whether the three cation sites are occupied by cations, or only two out of three, one distinguishes two groups from phyllosilicates: trioctaédriques and dioctaédriques.

The layer O isolated form also from minerals, and in particular from the hydroxides: the Brucite, Mg (OH) ₂, trioctaedric, and Gibbsite, Al (OH) ₃, dioctaedric.

According to the type of layer, the phyllosilicates are classified in the following groups:

• Phyllosilicates TO or 1: 1, where the layer is made of a layer T and a layer O, the thickness of the layer being approximately 7Å: group Kaolinite - Serpentine;

• Phyllosilicates EARLY or 2: 1, where the layer is made of two layers T in the two sides of a layer O, the thickness of the layer being approximately 10Å: group Talc - Mica - Montmorillonite whose many minerals are the principal components of the Argile S;
• Phyllosilicates EARLY: O or 2: 1: 1, where the layer is made of three layers EARLY and another layer O isolated, the thickness of the layer being approximately 14Å: group Chlorite S.