Table 1. Composition of manganese crusts from the Atlantis Fracture Zone

Summaries of the transition element chemistry of oceanic ferro-manganese deposits report compositional trends related to water depth and to geographic proximity to continental margins1-4. Explanations of compositional variations include continental source influence3, 5, 6, diagenetic environmental control of manganese mineralogy that regulates the trace metal composition1, 3, 7, ionic mobility in interstitial solutions during diagenesis3, 8-10, and volcanic or hydrothermal influence3, 11-14. Glasby15 rejects a significant pressure control on manganese oxide mineralogy on thermodynamic grounds.