Chapter 5. Structure and microstructure of serpentine minerals
by Marcello Mellini
The basic serpentine structure is extremely simple. In spite of the simple crystalchemical features involving the nearest neighbours (namely, the coordination polyhedra), complexity arises because of the different ways in which the basic polyhedra assemble together, forming flat layers in lizardite, curled layers in chrysotile, alternating layers in antigorite, flat kinked layers in polygonal serpentine, and flat geodesically kinked layers in polyhedral serpentine.
Further complexity is derived from not-nearest-neighbour relations, such as polytypism and polysomatism, that may occur as ordered and disordered distributions. A peculiar feature of chrysotile and polygonal serpentine is the presence of local fivefold symmetry. Chrysotile shares many nanoscale properties with synthetic nanotubes and nanowires.
Serpentine minerals may be mutually associated, or interleaved with other layer silicates. Serpentinization and deserpentinization reactions have important implications for many extremely important large-scale processes occurring in the Earth’s crust and outer mantle.
Due to their occurrence as tiny disordered crystals, meaningful structural study of serpentine minerals deals mostly with the nanoscale and may require alternative, unconventional methods. For this reason, electron microscopy techniques have long been used widely in the study of serpentine minerals, revealing a fascinating microstructural world.
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