Including anhydrous and hydrous(18 crystal water) type. Usually, the crystal separated out from aqueous solution at the normal temperature is Al 2 (SO 4 ) 3 .18H 2 O; when weathering, the average molecular structure is Al 2 (SO 4 ) 3 .14H 2 O, may appear white powdery, with bright flake or crystalline flakelet, odorless, to change the taste from sweetness to slight astringency