For example,
Germanium and Silicon with both Mohs(scratch) hardness of 6 and 7 respectively. But they also have the same tetrahedral structure.
I've seen some answers such as,
(a) The covalent bonds between carbon atoms produces the hardness, this is why silicon and germanium produce lower hardness.
(b) because it has the most tightly packed arrangement of atoms within the lattice, so bond lengths are the key parameter here.
I can also see it being a combination of both, but I don't see a clear answer, some have mentioned the combination, and others specifically the covalent bonds between the carbon atoms.
Why is it we have diamond lattices in other elements/materials, but no similar physical characteristics of diamond seen in those materials?
Thank you for your help And let me know if this is a question for another stack exchange
Related : Why are silicon-silicon bonds weak?
