Describe the structure of pyroxenes (see page 986). What is the ratio of silicon to oxygen in this type of silicate?

Data given in page 986

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Six-member rings of Si atoms with O atoms in edges are a common structural element in silicates. "Books" of mica are stacks of silicate sheets. Figure 21.23 Mica, a sheet silicate. The sheetlike molecular structure of mica explains its physical appearance. As in the pyroxenes, each silicon is bonded to four oxygen atoms, but the Si and O atoms form a sheet of six-member rings of Si atoms with O atoms in each edge. The ratio of Si to O in this structure is 1 to 2.5. A formula of SiO2.5 requires a positive ion, such as Na+, to counterbalance the charge. Thus, mica and other sheet silicates, and aluminosilicates such as talc and many clays, have positive ions between the sheets. John C. Kotz