Based on transmission electron microscopy and electron diffraction observations, we report the discovery of nanocrystalline botanical magnetite in iron-rich extracts from disrupted grass cells. The majority of the magnetite nanocrystals extracted from the grass plants display cubo-octahedral shapes, with a minority of hexagonal prism morphologies. In addition to the constrained morphologies, each group has a narrow size distribution typical of intracellular-boundary organized biomineralization processes responsible for bacterial magnetite. The smallest cubo-octahedral botanical nanocrystals (4 ± 1 nm) are an order of magnitude smaller than their bacterial counterparts. These botanical nanocrystals are self-organized in ordered, micrometer-sized agglomerates, distinct from magnetite strings in magnetotactic bacteria and similar to some pedogenic magnetite currently attributed to inorganic processes. We discuss the implications of our findings on the search for magnetite records of extraterrestrial and ancient terrestrial life, the origin of the terrestrial topsoil magnetite, and the potential for bioremediation using botanical magnetite.

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