why or how is diamond stronger than silicon dioxide?

Diamond is made up of a huge number of C-C bonds, while silicon dioxide is made up of a huge number of Si-O bonds.

Carbon (C: 2, 4) and oxygen (O: 2, 6) are Periodic 2 non-metals in the Periodic Table, while silicon (Si : 2, 8, 4) is in Period 3. Therefore, the size of silicon is larger than that of C or O, and thus the bond length of C-C bond is shorter than that of Si-O bond.

The shorter the bond length, the stronger the covalent bond is. Therefore, C-C bond is stronger than Si-O bond. This comes a conclusion that diamond is stronger than silicon dioxide.