The crystal structure of green rust can be understood as the result of inserting the foreign anions and water molecules between brucite-like layers of iron(II) hydroxide, ().  The latter has an hexagonal structure, with layer sequence AcBAcB... , where A and B are planes of hydroxide ions, and c those of  (iron(II), ferrous) cations.   In the green rust, some  cations get oxidized to  (iron(III), ferric).  Each triple layer AcB, which is electrically neutral in the hydroxide, becomes positively charged.  The anions then intercalate between those triple layers and restore neutrality.
There are two basic structures of green rust, "type 1" and "type 2".  Type 1 is exemplified by the chloride and carbonate varieties.  It has a rhombohedral crystal structure similar to that of pyroaurite.  The layers are stacked in the sequence AcBiBaCjCbAkA ...; where A, B, and C represent  planes, a, b, and c are layers of mixed  and  cations, and i, j, and k are layers of the intercalated anions and water molecules. The c crystallographic parameter is 22.5–22.8 Å for the carbonate, and about 24 Å for the chloride.
Type 2 green rust is exemplified by the sulfate variety.  It has a hexagonal crystal structure, with layers probably stacked in the sequence AcBiAbCjA...