Editorial Feature

Maghemite – Occurrence, Properties, and Distribution

Jun 3 2014

The term maghemite was derived from two known minerals, magnetite and hematite. The term is also an allusion to the mineral’s magnetic quality. It belongs to the family of iron oxides.

Properties of Maghemite

The following are the key properties of maghemite:

Cell Data
- Space group: P4₁32 or P4₃32 (synthetic)
- a = 8.3515(22)
- Z = 8 (for Fe_2.67O₄)
- Space group: P41 or P43 (synthetic)
- a = 8.35
- c = 24.99
- Z = 32

Crystal Data
- Cubic, mostly with a tetragonal supercell
- Point group: n.d.
- Rarely as minute octahedral crystals, or acicular overgrowths
- Commonly as coatings on, or replacements of, magnetite
- Massive
- X-ray powder pattern: Synthetic; cubic
- 2.5177 (100), 2.953 (35), 1.4758 (34), 1.6073 (24), 2.0886 (16), 1.7045 (10), 1.0872 (7)

Chemical Composition

Elements	Content 1
Fe₂O₃	74.6
MgO	8.4
TiO₂	13.0
Al₂O₃	1.8
MnO₂	0.9
SiO₂	0.3
Total	99.0

Optical Properties
- Brown to yellow in transmitted light
- White to bluish-gray in reflected light
- Optical class: Isotropic
- R: (400) 31.5, (420) 30.2, (440) 25.8, (460) 27.6, (480) 26.6, (500) 26.0, (520) 25.5, (540) 24.8, (560) 24.0, (580) 23.2, (600) 22.4, (620) 22.0, (640) 21.6, (660) 21.2, (680) 20.8, (700) 20.4

Estimated Properties

Electron density	Bulk density (electron density) = 5.23 gm/cm³ note: Specific gravity of maghemite = 5.49 gm/cm³
Photoelectric	PE_Maghemite = 21.37 barns/electron U = PE_Maghemite x ρElectron density = 111.70 barns/cm³
Fermion index	Fermion index = 0.01 Boson index = 0.99
Radioactivity	Maghemite is not radioactive

How to Identify Maghemite

Maghemite can be identified in the field by its dark brown color and opaque form, with sub-conchoidal fractures and massive granular structure. This mineral has no cleavage, but it has uniformly similar crystals, forming large masses.

The density of maghemite is 4.9 g/cm³, with a hardness of 6 – approximate to orthoclase. It is magnetic in nature. The mineral has a metallic lustre, with brown streak.

Global Distribution

Maghemite is widely distributed in many parts of the world. Some of them are listed below:

Israel - Hatrurim Formation
South Africa - Bushveld complex, Transvaal
Germany - Katzenbuckel, Odenwald, Baden-W¨urttemberg
USA - Iron Mountain mine, near Redding, Shasta Co. California
Canada - Wabush Iron Formation, Labrador City, Labrador, Newfoundland; in the Steep Rock Lake iron deposits, Ontario; at the Baffinland Iron Mines, northern Baffin Island
Japan - Takanokura mine, Fukushima Prefecture; Ohinata mine, Nagano Prefecture; and Kumano mine, Yamaguchi Prefecture
Brazil - North of Patos de Minas, Minas Gerais

Occurrence of Maghemite and Useful Mineral Association

Maghemite occurs due to weathering, or low-temperature oxidation of spinels containing ferrous iron, common magnetite, or titanian magnetite. It is also found in the widespread yellow pigment in continental sediments, rocks, and soils.

It is often associated with minerals such as magnetite, pyrite, marcasite, ilmenite, goethite, anatase, and lepidocrocite.