6 
Nodules commonly contain more than 30 elements. In addition to the 
elements included in Table 2, there are also appreciable amounts of 
cadmium, tin, arsenic, and bismuth. 
MINERALOGY 
Petrographic examination of thin sections of nodules reveals ex- 
tremely fine-grained manganese and iron oxides. The two major man- 
ganese minerals that have been identified are todorokite and birnessite. 
Todorokite is variable in its chemical composition and can contain sig- 
nificant amounts of other elements, while birnessite is more highly 
oxidized and is most abundant in more oxidizing environments such 
as shallower water areas. 
The only iron mineral which has been recognized in ferromanga- 
nese nodules is goethite, FeOOH. Most of the other metals found in 
nodules appear to be taken up by the iron and manganese oxides either 
by substitution, absorption, or adsorption and do not form separate 
minerals. 
In addition to the minerals formed in place, there are considerable 
amounts of detrital minerals within the nodules. These include quartz, 
feldspars, rutile, calcite, montmorillonite, illite, and barite. These min- 
erals are also extremely fine-grained and usually are distributed 
throughout the entire nodule. 
Formation oF MAancanrse NopuLEs 
Several hypotheses on the formation of deep seabed manganese 
nodules have been presented, proposing organic or inorganic processes, 
or a combination of both. 
BIGLOGICAL ORIGINS 
Recent evidence seems to favor a major role by living organisms 1n 
the creation of manganese nodules.? Small tubular structures have 
been found on the surface of carefully collected nodules. These fragile 
structures are built from microglobules of manganese by foraminifera 
and other bottom-dwelling organisms. Some tubes originally con- 
structed on nodule surfaces are found buried or preserved within the 
interior of nodules. The interior tube-remains are filled with clay or 
other debris and with manganese precipitated by inorganic or bacterial 
processes. In a sense, nodules may grow in much the same way as coral. 
Other evidence has been found which indicates that maganese oxides 
can precipitate and accumulate onto a growing nodule without bac- 
teria, but that bacterial enzymes accelerate the process through a cat- 
alytic role.* Iron oxides and copper, nickel, and other metals probably 
precipitate inorganically, since they are known to adsorb strongly on 
manganese oxide. Manganese oxidizing bacteria have been found to 
promote the growth of nodules by manganese accretion, whereas 
3Greenslate, J. Microorganisms Participate in th i . 
Wee ia oe ro ouEan icipate in the Construction of Manganese Nodules 
4Ehbrlich, H. L. The role of microbes in manganese nodule genesis and degradation. In 
Perromanganese Deposits on the Ocean Floor, Horn, D. R., ed., IDOE National Science 
Foundation, Washington, D.C., 1972 : 63-70. 
