Sehr geehrter Herr Günther,

Illite in its pure modification should have 10 Anström (=A) mica-like layers. Brammallite the Na modification should have 9.77 A. One of the big problems lies in the purity of this phyllosilicate which always may have chlorite and/or smectite interlayers. I only know one illite deposit in Hungary which has rather high-grade illite. This is the answer of an economic geologist dealing with argillaceous raw material, a clay mineralogist might certainly give you a more precise answer.

Ich wünsche Ihnen viel Erfolg

H.G.Dill

A decrease in layer charge was not required for K exchange, but a decrease did occur in K-depleted biotite and vermiculite, l~Iuscovite with the highest layer charge (247 meq/100 g), least expansion with Na (12.3~), and least sensitivity to solution pH had the highest selectivity for K and the slowest rate of exchange. The K in vermiculite was the most readily exchangeabIe. ..The valence of the cations has the larger impact on the behaviour of clay–water systems. The differences in size and hydration energy of K+, Na+ and Ca2+ ions have strong implications for the structure of interlayer. This leads to the differences in the layer spacings of the simulated K+-, Na+-, and Ca2+-montmorillonites. Furthermore, these simulations show that the K cations interact strongly with the clay sheets for the dehydrated clay sheets, but for the hydrated clays the Ca cations interact clearly strongly with the clay sheets

Sehr geehrter Herr Dill,

Dear Mr. Srivastava,

thank you for your valuable answers.

Increase in spacing occurs when illite is of trioctahedral nature (biotitic) and is reflected in XRD at spacing of 12.2 angstrom. Such increase does not happen with dioctahedral illite (muscovitic). You may refer to the following paper for details '

Pal, D.K. 1985. Potassium release from muscovite and biotite under alkaline conditions. Pedologie (Ghent) 35:133-146.

The simple answer is no, but only if its a straight replacement of unhydrated Na+ for K+ in which case the spacing will decrease rather than increase, but if hydration of the cation also occurs then the spacing would increase, this is why the 12.2 Angstrom spacing is observed in the study mentioned by Dr Pal.