Rhodium, one of the least abundant of the Pt-group elements in the ear
th's crust, has the second highest concentration in seawater. This may
be a consequence of strong complexing, perhaps kinetically restrained
with time constants of the order of centuries to millenia. The elemen
t shows a nutrient-like distribution in waters of the Pacific Ocean. P
elagic and coastal sediments have Rh concentrations close to crustal v
alues. There is a remarkable enrichment of Rh in ferromanganese minera
ls that cannot be explained by oxidative capture. Unlike the other Pt-
group elements, Rh is enriched in the high temperature hydrothermal su
lfide deposits as well as phosphorites.