Plesiotype series

In a plesiotype (rrATjcrto = near) series [2, 5], only the main features of the building modules and the principles of connection are preserved, but details of both the chemical composition and the configuration differ in the members of the series. Examples are given below, including mero-plesiotype series in which merotypy and plesiotypy occur at the same time. 

In terms of merotypy and plesiotypy, the bafertisite-type structures belong to a mero-plesiotype series [38]. This series is merotype because the HOH module is constantly present in the crystal structure of all members, whereas a second module, namely the interlayer content, is peculiar to each member. The series has also a plesiotype character because the (i) chemical nature and coordination number of the Ti and Y cations and (ii) the linkage between the H and O sheets are variable. The two H sheets sandwiching an O sheet either face each other via the same type of... 

MODELLING SEIDITE-(CE) - THE RHODESTTE MERO-PLESIOTYPE SERIES... 

Ce) was discovered to share its silicate module with rhodesite [65] (Figure 17-15) [K2Ca4[Si80i8(0H)]2.12H20 Pmam, a = 23.416, b = 6.555, c = 7.050 A] and related structures (see below) with which it forms a mero-plesiotype series. The... 

In conclusion, seidite-(Ce) and the mentioned rhodesite-like compounds form a mero-plesiotype series. Nearly the same (plesiotype aspect) double silicate layer occurs in all members and alternates with a variable octahedral module (merotype aspect). 

Plesiopjc seres. The crystal structures of the members of these series are based on modules which have common features but may contain additional peculiar details. The family of serpentine-like structures (lizardite, chrysotile, antigorite, carlosturanite) is an example reported by Makovicky (1997). The members of this plesiotypic series are based on variously curled, reversed and/or interrupted TO (serpentine) layers. 

The entire group of layer silicates could therefore be classified as a mero-plesiotypic series in the sense that both structural details and nature of the building modules varies. 

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. 

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

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