Light micrograph of iron-stained sideroblasts in human bone marrow, magnified 210x. Sideroblasts are atypical, abnormal nucleated erythroblasts (precursors to mature red blood cells) with granules of iron accumulated in perinuclear mitochondria. Ringed Sideroblasts are named so because of the arrangement of the iron granules in a ring form around the mitochondria.