II. COMPOSITION, FORMATION, AND DISTRIBUTION OF MANGANESE 
NODULES 
Ferromanganese nodules are concretions that occur on the ocean floor 
generally in water deeper than 2,000 meters. There are two dominant 
types of ferromanganese deposits: (1) thick slabs or crusts which 
frequently develop on submarine elevations where current activity 
prevents normal sediment accumulation and provides a continuous 
supply of metals, and (2) nodules which form at great depth around 
nuclei of rock, plant, or animal remains. The encrustations do not 
appear to be economically significant whereas some nodule deposits 
are potentially profitable to mine. Nodules are the most common form 
of seabed iron-manganese concretions. 
Ferromanganese nodules vary widely in shape, composition, surface 
texture, and internal structure. In individual localities the nodules 
are generally similar, but significant variations commonly occur from 
one locality to another. Variations may even be found over the dis- 
tance of a few hundred yards. Knowledge of variations in the com- 
position of the nodules is of importance to mining interests as most 
processing techniques are tailored to a fairly specific and uniform 
ore supply. Furthermore, some hydraulic mining techniques are de- 
signed to recover nodules within only a limited size range. 
SHAPE 
Nodules look like little black potatoes ranging in size from 1 to 15 
centimeters (cm) in diameter and average about 5 cm across. The gross 
shape of large nodules appears to be controlled by asymmetric growth 
rather than by the shape of the core or nucleus. 
(3) 
