Diaoyudaoite, as a new mineral, was discovered in marine deposite near Diaoyudao island, northeast of Taiwan, China. The idealized mol. formula is NaAl11O17 and its structural formula is represented by Na2O.11Al2O3. The crystal structure of a series of diaoyudaoite samples with different chromium contents was determine The structure is made up of layers of the double spinel unit and each layer is separated by a layer of sodium ions. The oxygen atoms are arranged in cubic close packing with the sequence ABCA. The hexagonal cell constants for the analyzed Diaoyudaoite samples are linearly related to the chromium concentration The replacement of aluminum by chromium is discussed.

Key words: CRYSTAL STRUCTURE DETERMINATION, ALUMINIUM ION, CHROME MINERAL, DIAOYUDAOITE