Answer
$SiO_{2}$ that is cooled slowly forms a tetrahedral structure called silica.
$SiO_{2}$ if cooled quickly forms a randomly ordered amorphous structure called a glass.
Work Step by Step
Silicon and oxygen form a network covalent structure in which a silicon atom bonds to four oxygen atoms, forming a tetrahedral shape with the silicon atom in the middle and the four oxygen atoms at the corners of the tetrahedron. The silicon atom bonds to each oxygen atom with a single covalent sigma bond. The silicon atom in this structure, by bonding to four oxygen atoms, obtains a complete octet. However, each oxygen atom is one electron short of an octet. Therefore, each O atom forms a second covalent bond to a different Si atom, forming the three-dimensional structure of quartz . Quartz has a formula unit of $SiO_{2}$ and is generally called silica.
After melting, if cooled quickly, silica does not crystallize back into the quartz structure. Instead, the Si atoms and O atoms form a randomly ordered amorphous structure called a glass. Common glass is amorphous $SiO_{2}$.
