Abstract: Eight samples of Co-rich ferromanganese crusts collected from the south west Indian Ridge have been analyzed for their mineralogy and geochemistry by using XRD and XRF methods. Based on the data, the genetic classification and the source of materials are further explored. The mineralogy of the crust suggests that Manganese minerals and Iron minerals are the main components of the crusts. Vernadite is the dominant component of manganese oxide with Todorokite the minor. The most abundant phase of the ferric minerals is X-ray amorphous FeOOH with Goethite identified by a weak X-ray peak. The concentration of Mn, Fe, Co, Cu, and Ni in the crusts ranges between the Pacific Ocean crusts and the Atlantic Ocean crusts or the Indian Ocean crusts, in an average value of 18.96%, 19.71%, 0.53%, 0.099% and 0.47% respectively. The Co-rich ferromanganese crusts are of hydrogenetic origin deduced from mineral composition, element groups and element ratios. The early diagenesis has slight impact on the crusts while the local hydrothermal effect has not been identified.