Magnet
A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Magnetosome
Magnetite crystals are encased in the magnetosome giving the MTB its magnetic properties. These crystals an either be made of iron oxide or sulfide. The MTB may either have iron oxide or sulfide but not both. Certain subgroups of the Proteobacteria in the domain of Bacteria have been found through analyses of the MTB’s RNA to only use iron oxide which is the more common material. Another smaller subdivision of the Proteobacteria that are part of a sulfide reducing bacteria use iron sulfide. Scientists say this suggests independent evolution of the same trait. The magnetite crystals have been observed in three different morphologies, cuboid, rectangular, and arrowhead shaped.