Unusual Fe-rich mineral formations were collected from the Calvert Cliffs area of Maryland. Surficial features such as wire-like filaments and columnar “chimneys” indicated a potential biological origin for the samples. Reference samples were collected from an Fe-rich acid mine drainage site near Carbondale, IL to serve as a comparison. The Chesapeake Bay samples were subjected to X-ray diffraction analysis, Scanning Electron Microscope-Electron Dispersive Spectroscopy analysis and Next-Generation Sequencing microbial assay. Minor ferrihydrite in the surficial wires and extensive microcrystalline goethite throughout the rest of the samples indicates a relatively recent origin. The small particle size and unusual microscale morphologies of iron (oxy)hydroxides and the presence of birnessite suggest that microbial metabolism was involved in the formation of these Fe minerals. EDS data indicate a strong relationship between Fe and C, as well as between Fe and P, while a lack of inorganic phosphate and carbonate minerals also indicates biological input. Genetic analysis reveals distinct internal and external microbial communities and the most common taxon within the sample interior was a novel bacterial phylum, indicating the mineralization may be a product of previously undescribed metabolic pathways. The presence of SO4- reducing, nitrogen-reducing and Fe-oxidizing bacteria as described by NGS analysis lends support to a microbially-mediated origin. Microbially driven oxidation of Fe and minor Mn into metal hydroxides is the proposed formation mechanism.