The structure of silicate minerals

Most of the Earth's crust is composed of silicate minerals, for example feldspars, and quartz, which crystallized from magma or formed deep in the crust, at high temperature and pressure during metamorphism. Silicate minerals are compounds principally of silicon (Si) and oxygen (O), combined with other metals. The basic building block of silicates is the SiO4 tetrahedron, in which silicon is situated at the centre of a tetrahedron of four oxygen ions (Fig. 4.2). This arrangement of ions is caused by the attraction—and strength of bonding—between positively charged and negatively charged ions (see Section 2.3), and the relative size of the ions —which determines how closely neighbouring ions can approach one another (Section 4.2.1).

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