The transitions from low to high temperature modificationsĪre: a-b-quartz, 5738 a-b-tridymite, 110–1808 and a-b-cristobalite,Ģ18 2 C. Silica glass is found in natureĪs obsidian. ( 1,500 C) to form crucibles, boats, etc., that are useful as containersīecause of the small coefficient of thermal expansion, and they are Than melting at a sharp melting point as crystals do. Liquid silica does not readilyĬrystallize but solidifies to a glass. The three forms are not readily interconvertible, and all three are foundĪs minerals. The three polymorphic structures and their temperature ranges are shown below.
Temperature form (a) and a high temperature form (b). Three polymorphic structures of silica, and each of these has a low Even though the basis of the structures is very simple, there are SiO2 requires that each oxygen atom is shared by two tetrahedra in Those of metal silicates) have only SiO4 tetrahedra, and the 1:2 ratio of The formula for silica is very simple-SiO2.
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