In geology, a rounded mineral concretion that is distinct from, and may be separated from, the formation in which it occurs. Nodules usually are elongated and have a knobby irregular surface; they are generally oriented parallel to the bedding. Chert and flint, clay ironstone, and phosphorites commonly occur as nodules. Manganese-rich nodules are found on the ocean floor.
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Manganese nodules grow by rain from above; the rain of plant and animal remains falling into the deep sea not only provides metals to nodules but also determines nodule growth rates and composition.
Feb 10, 1984; Manganese nodules had always seemed unlikely geologic denizens of the deep. Solid tennis-ball-sized hunks of manganese and...