Several different morphologies (shapes) of MTB exist, differing in number, layout and pattern of the bacterial magnetic particles (BMPs) they contain.[16] The MTBs can be subdivided into two categories, according to whether they produce particles of magnetite (Fe 3O 4) or of greigite (Fe 3S 4), although some species[which?] are capable of producing both. Magnetite possesses a magnetic moment with three times the magnitude of greigite.[2]