Polysomatism

In the previous sections composition variation has been attributed more or less to point defects and extensions of the point defect concept. In this section structures that can be considered to be built from slabs of one or more parent structures are described. They are frequently found in mineral specimens, and the piecemeal way in which early examples were discovered has led to a number of more or less synonymic terms for their description, including intergrowth phases, composite structures, polysynthetic twinned phases, polysomatic phases, and tropochemical cell-twinned phases. In general, they are all considered to be modular structures. 

D. R. Veblen, Electron Microscopy Applied to Nonstoichiometry, Polysomatism and Replacement Reactions in Minerals, in Reviews in Mineralogy, Vol. 27, P. R. Busek, Ed., Mineralogical Society of America, Washington, DC, 1992, Chapter 6. 

Veblen, D. R. (1981). Non-classical pyriboles and polysomatic reactions in biopyriboles, pp. 189-236. In D. R. Veblen, ed. Amphiboles and Other Hydrous Pyriboles—Mineralogy. Reviews in Mineralogy, 9A. Min. Soc. America, Washington, D. C. 

Ferraris, G., Khomyakov, A. P., Belluso, E., and Soboleva, S. V. (1997). Polysomatic relationships in some titanosilicates occurring in the hyper-agpaitic alkaline rocks of the Kola Peninsula, Russia. Proc. 30th Internat. Geol. Congress 16, 17-27. 

Leonyuk, L., Babonas, G.-J., Maltsev, V., and Ribakov, V. (1999). Polysomatic series in the structures of complex cuprates. Acta Cryst. A55, 628-34. 

Examples of such materials have been known for a number of years in the mineralogical field, where the terms intergrowth phases , polysynthetic twinned phases , polysomatic phases and tropochemical cell twinning have been applied to describe the stmctures. In recent years, the application of electron microscopy has revealed the defect stmctnres of vast numbers of phases containing extended defects. In this section, some well-characterized examples chosen are chosen for illustration. 

Mellini, M., Ferraris, G., Compagnoni, R. (1985). Carlosturanite HRTEM evidence of a polysomatic series including serpentine. Amer. Mineral., 70, 773-81. 

Thompson, J. B. (1978). Biopyriboles and polysomatic series. Amer. Mineral., 63, 239-49. 

Thompson JB Jr (1978) Biopyriboles and polysomatic series. Am Mineral 63 239-249 Toledano JC, Pateau L, Primot J, Aubree J, Morin D (1975) Etude dilatometrique de la transition ferroelastique de I ortho phosphate de plomb monocristallin. Mat Res Bull 10 103-112 Torres J (1975) Symetrie du parametre d ordre de la transition de phase ferroelastique du phosphate de plomb. Phys Stat Sol B71 141-150... 

Van Tendeloo G, Ghose S, Amelinckx S (1989) A dynamical model for the P i-11 phase transition in anorthite, CaAl2Si20g I. Evidence from electron microscopy. Phys Chem Minerals 16 311-319 Van Tendeloo G, Zandbergen HW, Amelinckx S (1987) Electron diffraction and electron microscopic study of Ba-Y-Cu-0 superconducting materials. Sol Stat Comm 63 389-393 Veblen DR (1991) Polysomatism and polysomatic series A review and applications. Am Mineral 76 801-826... 

Examples abound, especially in minerals. A classic polysomatic series is given by the minerals that are formed by an ordered intergrowth... 

D. R. Veblen, Electron microscopy applied to nonstoichiometry, polysomatism and replacement reactions in minerals, Chapter 6 in ... 

D. R. Veblen, Polysomatism and poly somatic series a review and applications, Am. Mineral., 76, 801-826 (1991). 

Following the first case treating the polysomatic series of biopyriboles [4], structures of several groups have been described as members of the same polysomatic series (see below). 

In the survey of modularity reported in Chapter 1 of [2], a general description of the modular interpretation of crystal structures has been extensively discussed. In this chapter we consider only planar modules, and the examples are devoted to show the polysomatic, merotype and plesiotype aspects (see below) of some series that are important either methodologically or for their technological and mineralogical relevance. The possibility of exploiting the modularity to model unknown crystal structures is illustrated with some examples. 

The members of a polysomatic (signifying many bodies [4]) series are crystal structures based on the varied stacking of the same modules A, B, C, With reference... 

The raw structure model of nafertisite was obtained on applying the principles of the polysomatic series and modifying the structures of bafertisite and astrophyllite after noting the following. 

The successful modelling of the crystal structure of nafertisite, according to the principles of modular crystallography, indicated [25, 31, 32] to correlate via a polysomatic series the group of titanium silicates of which the stmctures are based... 

Bafertisite represents the member of the polysomatic series. The corresponding (HOH)g layer is the most versatile among the known /70/7 layers, being able to sandwich a various more or less complex interlayer contents an updated list of more than 30 minerals containing this layer is given elsewhere [33]. 

Relative to the (HOH)g layer, in a (HOH)j astrophyllite-type layer an M module is present between two B modules. The titanosilicates based on a HOH)p layer represent the members B M of the heterophyllosilicate B M polysomatic series and differ from each other only by polytypy (i.e. stacking of the layers) and the chemical nature of the A and Y cations [34, 35]. 

Palygorskite (T), and sepiolite (5) are the end members of a modular series named palysepiole (pa/ygorskite -f sepiohit) polysomatic series P S [47] kalifersite is the P Si member. Falcondoite [51] and loughlinite [52] differ from sepiolite only in the composition of the O sheet in the TOT ribbons the same situation holds for yofortierite [53] and tuperssuatsiaite [54] in comparison to palygorskite. 

Because the sepiolite framework is substantially modified, intersilite is in a plesiotype relationship with the palysepiole polysomatic series. 

A description of the palysepiole polysomatic series and related structures offers the opportunity to mention the main members of the lintisite series of which the crystal stmctures are based on three building modules. One of these modules is a cut of sili-naite [57] (NaLiSi205.2H20 C2/c, a = 14.383, b = 8.334, c = 5.061 A, 13 = 96.6°), a crystal structure that shows a chess-board arrangement of channels and ribbons comparable with that of palysepioles. Modules of silinaite (S) have been used [58] as one of three modules needed to describe the modularity in the lintisite group (Figure 17-14). The other two modules are slabs (L) of the structures of lorenzenite [59]... 

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