# Number of bridge oxygen atoms in a silicate mineral

Total number of oxygen atom(s) which act(s) as bridge between any two silicon atoms in a mineral with composition $$\ce{MM’Si3O_x}$$ $$(\ce{M}$$ is the divalent metal ion and $$\ce{M’}$$ is the tetravalent metal ion).

This is the question I have been stuck on. I do not understand how to approach it. Are we supposed to used the concepts of silicates? Like sheet silicate, chain silicate etc. or interstitial salts concepts?

Also, I don’t know whether it is possible to draw the structure as $$x$$ is a variable. Any hint would be appreciated.

Since $$\ce{M}$$ is divalent and $$\ce{M’}$$ tetravalent, they exist as $$\ce{\overset{2+}{M}}$$ and $$\ce{\overset{4+}{M’}},$$ respectively. The anionic part is $$\ce{[\overset{+4}{Si}_3\overset{-2}{O}_x]^6-},$$ and taking oxidation numbers into consideration, $$x = 9.$$ $$\ce{[Si3O9]^6-}$$ moiety implies cyclic metasilicates:
There are three bridging oxygen atoms per ring or per formula unit. A real life example for the mineral from the problem could be benitoite $$\ce{BaTiSi3O9}$$.