Chapter 20 presents an example of a relatively simple inorganic compound—nickel manganese oxide hydroxide, NiMnO2(OH)—which has, though not perfect, crystallinity. Due to the peculiar shape of the crystallites, which grow as well-defined, elongated faceted needles (see inset in Fig. 20.1), the powder shows a strong tendency toward complex preferred orientation. This is a complicating factor, particularly when solving the structure from first principles. This example also illustrates methods for detecting and refining hydrogen atoms from powder data, as well as for distinguishing Mn and Ni—a challenging task when relying solely on X-rays. Therefore, the refinement was completed using combined X-ray and neutron powder diffraction data.