Neso-silicates

Orthosilicates or neso-silicates Isolated [Si04] tetrahedra Olivine, (Mg, Fe, Mn)(Si04) Zircon, Zr(Si04)... 

Figure 5. Summary plot of apparent number of layers removed or extracted of silica (0-6 weeks) vs. estimated solubilities with respect to dissolved silica, juM, using the 0-6 week data in Figure 4(a-z). The diagonal dashed lines suggest general trends in the data, while the narrow solid line at 100 /xM is the mean concentration of dissolved silica in seawater. Brackets and various types of shading separate minerals into various groups phyllosilicates, crosshatching tectosili-cates, open inosilicates, diagonal lines neso- and soro-silicates, solid.

Mineralogica1 structural types may have an effect on silica release rates as has been mentioned earlier. That is, isolated silica tetrahedra and small units (neso-, soro-silicates) release silica more quickly than single or double chains (ino-silicates) which in turn are more reactive than three dimensionally linked tetrahedra (tec to-silicates) or tetrahedra arranged in sheets (phyllo-silicates). But such structures are not the only cause for variations in silica release rates. 

We need to digress briefly to examine the structures of some of the ions that are formed by the condensation of the nesosilicate ion, SiO/" (the word neso is from the Greek nesogaean meaning island. The nesosilicates are sometimes also referred to as insular silicates). Two SiOA ions can combine by sharing one oxygen to form the sorosUicate ion. This ion is shown below with two tetrahedra joined by one comer. 

Subclasses also exist and the most useful ones are probably the neso-, soro-, cyclo-, ino-, phyllo-, and tecto-silicates which give some indication of the state of polymerization of SiOt tetrahedra into rings, chains, bands, sheets, networks, and so forth. 

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