Muscovite growth direction

In the dioctahedral 2 1 sheet-structure silicate with the occupied sites more than 85% occupied by Al, the structure seems to be able to compensate for the internal strain and can grow to a considerable size. The Al octahedral occupancy values of muscovite (>1.7) and the 2 1 dioctahedral clays (1.3—1.7) indicate that there is little overlap. It is likely that the decreased amount of tetrahedral twist induced by increasing the size of the octahedral cations and octahedral charge (decreasing Al) determines that a clay-size rather than a larger mineral will form. The R3+ occupancy value can be less than 1.3 when the larger Fe3+ is substituted for Al. When Al occupancy values are less than 1.3 (65%), in the absence of appreciable iron, the internal strain is such that growth is in only one direction. The width of the layer is restricted to five octahedral sites. Sufficient layer strain accumulates within this five-site interval such that the silica tetrahedral sheet is forced to invert to accommodate the strain. 

Figure 8.2 Growth substrate muscovite mica, (a) Top view. Red line indicates the grooved muscovite direction. Arrows show surface electric fields, which are connected to the groove direction. Rectangle indicates the surface unit cell.

For the investigated rod-like molecules so far the possible needle directions on muscovite depend on the epitaxial orientation of the molecules on the substrate, and on the packing of these molecules within a needle [24], Therefore para-functionalized para-phcnylcncs show a very similar growth behavior compared to p-6P. The a-thiophenes quaterthiophene and sexithiophene, however, align with their long molecular axes along the two muscovite high symmetry directions without... 

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