Abstract: An isomer of ammonium octamolybdate (“AOM”) and method for producing the same. A new AOM isomer (“X-AOM”) is described which is characterized by a distinctive Raman spectral profile compared with other AOM isomers including &agr; and &bgr;-AOM. To produce the novel isomer, ammonium dimolybdate (“ADM”) is combined with molybdenum trioxide (MoO3) and water to yield a mixture. When mixing these materials, optimum results are achieved if at least one of the foregoing molybdenum-containing reagents is added in a gradual, non-instantaneous manner so that the selected reagent is not added to the mixture in a single large mass. This gradual delivery procedure, along with a carefully controlled prolonged heating stage (e.g. in excess of 3 hours) contributes to a maximum yield of high purity X-AOM.