Structural features of todorokite intergrowths in manganese nodules

The disordered, cryptocrystalline phases that comprise manganese nodules^1,2 typically yield broad, diffuse X-ray lines that have led to ambiguity in their identification. Of particular interest is the manganese oxide phase that has been correlated to the presence of copper and nickel in nodules. This host phase has a characteristic X-ray d-spacing of ∼10 Å and has been compared with both a naturally occurring material - todorokite^3,4 - and a synthetic phase - buserite^5,6. The structures of those phases have been difficult to decipher, but recent work using high-resolution transmission electron microscopy (HRTEM) has provided insight into the todorokite⁷ and buserite⁸ structures. Using HRTEM results we now show that the nodule 10 Å phase does have the same structure as non-marine todorokite⁹. In addition, structural imaging shows that both nodule and non-marine todorokite exhibit similar disordering phenomena. A unique feature of the nodule todorokite is its intimate and topotactic intergrowth with a possible double-chain oxide. Its paragenetic relationship to todorokite is not yet determined.