Quote Originally Posted by Herpestidae View Post
I now wait to see my ass-pullery get shot to hell and back
Glad to oblige.
Shells are composed of many things, but chitin and calcium carbonate are major components. Neither of those are silicates. (Heck, one is a carbonate.) I am not a biologist.
Additionally, there is a world of difference between diamond and a carbonate. Compare diamond with graphite and even coal. All three are composed of carbon, but they are very different. It depends on how the carbon bonds together, in graphite it forms layers of hexagons, in carbon it forms a cubic lattice, and it coal it forms a huge mess with numerous other elements attached wherever. Diamond is strong because of the lattice shape it forms, not because it contains carbon. And as a carbonate is already stuck with 3 oxygen atoms (it's CO32-), it can't form the lattice. I am not a chemist.
Also note that while diamond is hard, it is not particularly tough, so can be shattered. Not so useful for armour.