![]() For example, in the transformation of smectite to illite, the percentage of illite layers increases with temperature, geological time, and water/rock ratio, and accordingly the layer stacking mode shifts from R0 (random) to R1 (alternating), and then to longer-range order (R3) 4. Under certain conditions, clays tend to form mixed layers with complex layer stacking patterns (see 7 and refs. The PBCs theory may provide a plausible explanation for the fibrous nature of some clay minerals such as sepiolite, but it fails to explain other key features of clay minerals such as the great dimensional disparity between illite and muscovite in spite of both minerals possessing a similar structure 6. Depending on cation ordering and occupancy in octahedral and tetrahedral sheets, crystal defects may tend to concentrate and thus poison crystal growth along one, two, or three PBCs, therefore limiting crystal dimensions in growth. Based on the Periodic Bond Chains (PBCs) theory, Meunie 1 suggested that the size and shape of a single clay platelet might depend on the amount of crystal defects along the three axes of symmetry, \(\). The dimension disparity between the two directions can be up to 200 times 1. The a- b dimension of clay crystallites ranges from a few nanometers to micrometers 4, while the dimension along the c-direction ranges from \(\sim 1\) to \(\sim 100\) nm 3, 5. Clay are known for their small particle sizes and high density of defects 3. The Si and Al centers in the layers can partially be substituted by lower-valent metals, resulting in negative charges in the layers, which are then balanced by interlayer cations 2. ![]() The thickness of a 2:1 layer is about 0.65 nm 1. smectite and illite) phyllosilicate layers. 1), in which one aluminum oxide octahedral sheet joins with one or two silica tetrahedral sheets to form what is called 1:1 (e.g. Clays are layers of aluminosilicates (Fig. Clay minerals provide a useful model system for studying a transition from a 1D to 3D system in crystal growth and for a nanoscale structural manipulation of a general type of layered materials.Ĭlays are ubiquitous in the Earth system, especially in sedimentary and weathering systems. This treatment allows for a systematic prediction of clay particle size distributions and layer stacking as controlled by the physical and chemical conditions for mineral growth and transformation. The layer stacking or ordering in an interstratified clay can be described by a 1D Ising model while the limited extension of individual phyllosilicate layers can be related to a 2D Berezinskii–Kosterlitz–Thouless transition. Because of its weak interlayer interaction, a clay mineral can be treated as two separate low-dimensional systems: a 2D system for individual phyllosilicate layers and a quasi-1D system for layer stacking. We show here that the limited dimension of clay particles arises from the lack of long-range order in low-dimensional systems. Clays are known for their small particle sizes and complex layer stacking.
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