Feroxyhyte is an oxide/hydroxide of iron, δ-Fe<sup>3+</sup>O(OH). Feroxyhyte crystallizes in the hexagonal system. Feroxyhyte forms as brown, rounded to concretionary masses. Feroxyhyte is an opaque, magnetic mineral with a yellow streak and a relative density of 4.2. Forms under high pressure conditions and reverts to goethite on exposure to surface conditions.