We used the X-ray diffraction method to determine systematically the mineral phases in bulk sediment samples and acid undissolved residuals of the fine-grained fraction of the surface sediments from the 49.6°E hydrothermal field at the Southwest Indian Ridge (SWIR) and discussed the mineral sources of the surface sediments. The results showed that the surface sediments in this region were composed of calcareous ooze, and calcite was the dominant mineral. The sediments also contained quartz, feldspar, clay minerals, pyroxene, sphalerite, barite, serpentine, and magnetite. The quartz, feldspar, and clay minerals were exogenous minerals that mainly originated from the Namib and Kalahari deserts in southern Africa. The pyroxene, serpentine, magnetite, sphalerite, calcite, and barite were endogenous minerals from weathering of seafloor basement rocks and seafloor hydrothermal activities. The sulfide particles in the sediments were mainly deposited from upwelling plumes.