Hello,

The difference of both minerals can partly be seen as different degree of crystalization – usually crystals are better expressed at kaolinite than montmorillonite, and the syngony is slightly different. But this differentiation is usually difficul, therefore you better use EDS mode, and difference in chemical composition will for sure help you to differentiate the two minerals. Kaolinite contains much more alumina (around 40 % Al2O3) than montmorillonite (around 20 % Al2O3, together with some sodium and calcium). You can easily find some more data on the web (webmineral.com).

Best wishes,

Mirka 

1.Kaolinite

-1:1 (1 aluminium octahedral sheet and 1 silica tetrahedral sheet)

-The sheets are held together by van der waals bonds and the hydroxyls of the octahedral sheet.

- Layers are held together by hydrogen bonding which restricts expansion and limits the reactive area to external surfaces.

- High swelling capability

- Low charge and low cation exchange capacity.

- Larger in size than montomorillionite ( 0.1-0.5)

2. Montomorillionite

- 2:1 ( 2 silica tetrahedral sheets and 1 alumina sheet)

- The adjacent layers are joined by van der waals bonds.

- High expansion

- High cation exchange capacity (0-120)

- Smaller in size ( 0.001-0.1) thus higher surface area compared to Kaolinite

Please read the following article which include images of SEM of different clays and clay minerals including kaolinite and Montmorillonite clays.

http://www.clays.org/journal/archive/volume%2019/19-1-49.pdf

Larger particles include kaolinites and smaller montmorillonite particles

Large sheet-like lamellas are kaolinite and small strands are montmoriollinite.

Also, according to XRF data. Montmorillonite is high in SiO2, Al2O3 and Na2O contents but very low in other major oxides.