How many corners of SiO ₄ units are shared in the formation of three dimensional silicates?

Step-by-step solution

If all the four corners, i.e., all the four oxygen atoms of each tetrahedra ( SiO ₄ ) are shared with other tetrahedra, three-dimensional network structure is obtained. i.e., different forms of silica such as quartz, tridymite and crystobalite.