Feroxyhyte

Feroxyhyte is an oxide/hydroxide of iron, δ-Fe³⁺O(OH). 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.^[3]

Feroxyhyte
Image of Feroxyhyte
General
Category	Oxide mineral
Formula	δ-Fe3+O(OH)
IMA symbol	Fox[1]
Strunz classification	4.FE.40
Dana classification	06.01.04.04
Crystal system	Hexagonal Unknown space group
Unit cell	a = 2.95, c = 4.56 [Å]; Z = 1
Identification
Formula mass	88.85 g/mol
Color	Brown, yellow-brown
Crystal habit	Concretionary, massive, nodular
Streak	Yellow
Diaphaneity	Opaque
Specific gravity	4.31
Density	4.2
Optical properties	Uniaxial
References	[2][3][4]

It occurs in manganese-iron nodules on the Atlantic and Pacific Ocean floors. It is also found in the Baltic, White, and Kara Seas.^[5] Forms under high pressure conditions and reverts to goethite on exposure to surface conditions.^[3] It also occurs as cement and coatings on clasts in poorly drained soils and sediments, formed by the rapid oxidation of iron(II) oxide compounds.^[5]

It was first described in 1976 for an occurrence in soils at its type locality: Kolomyya, Ivano-Frankivsk Oblast, Ukraine.^[2][5]