Answer:
Step-by-step explanation:
Because of their structure . Silica has a chain structure with e one silicon atom bonded to 4 oxygen atoms in the lattice. The structure is a long chain of tightly held atoms and this forms a solid.
The carbon dioxide molecule however as a linear structure and each oxygen atom is bonded by double bonds. These double bonds are not as strong as the Si - O bonds in silica so will not form a chain structure.