Answer
Pyroxenes are silicon tetrahedron structures in which many of the tetrahedrons bond together creating chains. The formula unit for these chains is the $SiO_{3}^{2-}$ unit, and the repeating unit in the structure is two formula units ($Si_{2}O_{6}^{4-}$).
Work Step by Step
Pyroxenes are silicon tetrahedron structures in which many of the tetrahedrons bond together creating chains. The formula unit for these chains is the $SiO_{3}^{2-}$ unit, and the repeating unit in the structure is two formula units ($Si_{2}O_{6}^{4-}$). Two of the oxygen atoms are bonded to two silicon atoms (and thus to two other tetrahedrons) at two of the four corners of each tetrahedron. The silicate chains are held together by ionic bonding to metal cations that lie between the chains.
