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 Fe2.67O4)
- 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
- 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
- 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
||Bulk density (electron density) = 5.23 gm/cm3
note: Specific gravity of maghemite = 5.49 gm/cm3
||PEMaghemite = 21.37 barns/electron
U = PEMaghemite x ρElectron density = 111.70 barns/cm3
||Fermion index = 0.01
Boson index = 0.99
||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.
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.