Analyses of small samples extracted from different parts of a single manganese nodule have been reported by several investigators, clearly documenting the belief that a nodule is not homogeneous chemically, as a rule. The same sort of evidence has been gathered by use of the X-ray macroprobe and electron microprobe analyses. The X-ray probe work has shown clearly that chemical variations within a nodule can be correlated with optically recognizable mineral,and therefore optical study can tell much about chemical variations and obviate much probe analysis. As we have reported many times, optically anisotropic crystalline todorokite and birnessite contain the bulk of the Mn, Ni, and Cu in any nodule whereas optically isotropic and X-ray amorphous oxides contain most of the Fe and Co in the same nodule.

From 1983 until 1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions. At the time it was the most extended data compilation on ferromanganese deposits world wide. Initially published in a proprietary format incompatible with present day standards it was jointly decided by AWI and NOAA to transcribe this legacy data into PANGAEA. This transfer is augmented by a careful checking of the original sources when available and the encoding of ancillary information (sample description, method of analysis...) not present in the NOAA-MMS database.

Supplement to: Fewkes, Ronald H (1976): Electron probe microanalysis of manganese nodules. Washington State University, 71 pp