Abstract
BLACK, hydrated ferromanganese oxide (FMO) concretions of microscopic to macroscopic size and complex mineralogy cover ocean floors all over the world at depths of up to 8 km (ref. 1). These amorphous–crystalline nodules have a total Cu, Ni and Co content of 40 p.p.m. to 4% and vary greatly in trace element content, apparently because of varying growth rates caused by the different Eh and pH in their environments. Black, amorphous, hydrated desert varnish (DV) coatings, 10–100 µm thick, are extensively found in limited areas of the world's arid lands2,3 in both the subtropics and in non-sterile areas of the Antarctic dry valleys4. Marine FMO nodules are formed principally by biological fixation processes; the mode and rate of formation of DV, on the other hand, are not understood, but concern anthropologists in their efforts to date petroglyphs and other artefacts of ancient man5.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
