Four manganese nodules collected south and southwest of Rarotonga one of the Cook Islands were subjected to microprobe analysis in order to determine variations in chemical composition between the concentric laminations making up the nodules. Nodules of maximum diameter of about 2.5 cm or less were selected so that the entire nodule could be sectioned for one probe mount. Probe mounts were prepared by vacuum embedding in cold-setting, clear-casting resin. Cutting and polishing were then performed using standard polished section techniques. The electron microprobe mounts were examined with a reflected light microscope in the microprobe, and 2 micrometer spots were selected for analysis along a line of traverse going through the centre (nucleus) of the nodule. Due to the fact that optically-reflective metal-rich layers were selected for analysis and darker detrital inclusions and silicate-rich layers were not analysed here the microprobe values are generally higher for Mn, Ni, Cu and Co, and lower for Fe, than the bulk chemical analyses.

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1989 NOAA-NCEI compiled the NOAA-MMS Marine Minerals Geochemical Database from journal articles, technical reports and unpublished sources from other institutions.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.This dataset represents the digitized Table XIV, pp. 175-176, of the related publication.