Maghemite

Maghemite
Maghemite from Gancedo, Chaco Province, Argentina
General
Category	Oxide minerals
Formula (repeating unit)	γ-Fe2O3
Strunz classification	4.BB.15
Crystal system	Cubic with a tetragonal supercell
Crystal class	Gyroidal (432) (same H-M symbol)
Space group	P4132, P4332
Unit cell	a = 8.33 Å; Z = 8 or a = 8.35 Å c = 24.99 Å; Z = 8 for tetragonal supercell
Identification
Color	Brown, bluish black; brown to yellow in transmitted light; white to bluish gray in reflected light.
Crystal habit	Rarely as minute octahedral crystals, or acicular overgrowths; commonly as coatings on or replacements of magnetite; massive.
Cleavage	None
Fracture	Subconchoidal
Mohs scale hardness	5
Luster	Dull
Streak	Brown
Diaphaneity	Opaque, transparent in thin fragments
Specific gravity	4.860 (calculated)
Optical properties	Isotropic
Other characteristics	Strongly magnetic
References

Maghemite (Fe₂O₃, γ-Fe₂O₃) is a member of the family of iron oxides. It has the same spinel ferrite structure as magnetite and is also ferrimagnetic.

Maghemite can be considered as an Fe(II)-deficient magnetite with formula ${\displaystyle \left({\ce {Fe^{III}8}}\right)_{A}\left[{\ce {Fe_{40/3}^{III}\square _{8/3}}}\right]_{B}{\ce {O32}}}$ where ${\displaystyle \square }$ represents a vacancy, A indicates tetrahedral and B octahedral positioning.