Summary of 3 main clay minerals

1. Clay Minerals (Phyllosilicates)
Groups of phyllosilicates: Clay minerals, Serpentine minerals, Pyrophyllites, Talc, Micas, Chlorite group minerals. Formation of clay minerals:
The type of clay mineral that forms from weathering will depend on:
Fluid rock ratio||pH of fluid||Priginal composition of weathered rock||Reaction rates
Kaolinites (1:1) – Non expanding
Smectites (2:1) – Expanding
Illites (2:1) – Non-Expanding
Chlorites (2:1:1) – Non- Expanding
 1 silica tetrahedron : 1 alumina octahedron
 No interlayer activity
 no shrink-swell
 little isomorphous substitution (replacement of cation of same size while crystal is growing)
 H-bonding holds sheets tightly together
 most common clay mineral
 Examples are Kaolinite, Dickite, Nacrite, and Halloysite
 2 layers of Si sheets (tetrahedral) on both sides of Al sheet (octaahedral).
 ‘Di’ (In case of Al3+ i.e 2 Al ions in octahedral layer) or ‘Tri’ (incase of Mg2+ i.e 3 Mg ions in octahedral layer) octahedral.
 Montmorillonite, nontronite, and beidellite (all dioctahedral).
 Saponite and palygorskite (trioctahedral)
 Water can also move in and out therfore large shrink/expansion.
 Large internal surface.
 Ca and Mg can move into the octahedral layer.
 Net negative charge but neutralized due to movable (attraction) cations e.g Ca2+, Mg2+.
 They absorb Oil.
 2 silica sheets : 1 alumina sheet
 Mostly dioctahedral minerals with interlayer K.
 Nonexpanding
 Common in shales.
 High net negative charge balanced by K+.
 Al3+ and K+ substitute for Si4+ (tetrahedral sheet).
 Some substitution of Mg for Al in octahedral layer leads to permanent negative (-) charge.
 weathering at edges = release of K+.
 Can form from smectites by the addition of K+.
 Interlayer is Mg6(OH)12 (brucite).
 Brucite allows for strong H-bonding between layers.
 Possible substitution in brucite layer can by Al3+, Fe3+, Fe2+ for Mg2+.
 Nonexpanding.
 Iron rich.
Brucite
Jahanzeb Ahsan