Feroxyhyte is an oxide/hydroxide of iron, Fe³⁺O(OH). It occurs in manganese-iron nodules on the Pacific Ocean floor. Forms under high pressure conditions and reverts to goethite on exposure to surface conditions. Feroxyhyte crystallizes in the hexagonal system. It forms as brown rounded to concretionary masses. Feroxyhyte is opaque, magnetic, has a yellow streak, and has a relative density of 4.2.