Soro-silicates

Disilicates or soro-silicates Discrete [Si207] units formed by two [Si04] tetrahedra sharing a common oxygen Thortveitite, Sc2(Si207) Hemimorphite, Zn4(0H)2(Si2O7)H2O... 

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. 

Pyrosilicates (Si207)6- - soro-silicates, Disilicates Two tetrahedral units are joined by sharing the O at one comer, thus giving (Si207)6-. The structure possessed by them are called island silicates stmcture(Fig)... 

The literature data for ortho-, soro-, ino-, and phyllosilicate dissolution at 25 °C derived from long duration dissolution experiments (> a month except for wollastonite and forsterite. Tables 3 and 5) bracket the value of the order with respect to H, n (see Equation (17)), between 0 and 0.85 at 25 °C. The higher values of n from the literature tend to be for silicates containing iron. Extrapolating the rate constant for the proton-promoted dissolution rate constant to other temperatures, h(T), can be accomplished with the Arrhenius equation ... 

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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