Iron(III) oxide

Iron(III) oxide
	; Fe O
Names
	IUPAC name Iron(III) oxide
	Other names ferric oxide, haematite, ferric iron, red iron oxide, rouge, maghemite, colcothar, iron sesquioxide, rust, ochre
Identifiers
CAS Number	1309-37-1 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:50819 ;
ChemSpider	14147 ;
ECHA InfoCard	100.013.790
EC Number	215-168-2;
E number	E172(ii) (colours)
Gmelin Reference	11092
KEGG	C19424 ;
PubChem CID	518696;
RTECS number	NO7400000;
UNII	1K09F3G675 ;
CompTox Dashboard (EPA)	DTXSID0029632 ;
	InChI InChI=1S/2Fe.3O [inchi] Key: JEIPFZHSYJVQDO-UHFFFAOYSA-N [inchi]; InChI=1/2Fe.3O/rFe2O3/c3-1-4-2(3)5-1 Key: JEIPFZHSYJVQDO-ZVGCCQCPAC;
	SMILES O1[Fe]2O[Fe]1O2;
Properties
Chemical formula	Fe2O3
Molar mass	159.687 g·mol−1
Appearance	Red solid
Odor	Odorless
Density	5.25 g/cm3
Melting point	1,539 °C (2,802 °F; 1,812 K); decomposes; 105 °C (221 °F; 378 K); β-dihydrate, decomposes; 150 °C (302 °F; 423 K); β-monohydrate, decomposes; 50 °C (122 °F; 323 K); α-dihydrate, decomposes; 92 °C (198 °F; 365 K); α-monohydrate, decomposes
Solubility in water	Insoluble
Solubility	Soluble in diluted acids, barely soluble in sugar solution; Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH
Magnetic susceptibility (χ)	+3586.0x10−6 cm3/mol
Refractive index (nD)	n1 = 2.91, n2 = 3.19 (α, hematite)
Structure
Crystal structure	Rhombohedral, hR30 (α-form); Cubic bixbyite, cI80 (β-form); Cubic spinel (γ-form); Orthorhombic (ε-form)
Space group	R3c, No. 161 (α-form); Ia3, No. 206 (β-form); Pna21, No. 33 (ε-form)
Point group	3m (α-form); 2/m 3 (β-form); mm2 (ε-form)
Coordination geometry	Octahedral (Fe3+, α-form, β-form)
Thermochemistry
Heat capacity (C)	103.9 J/mol·K
Std molar; entropy (S⦵298)	87.4 J/mol·K
Std enthalpy of; formation (ΔfH⦵298)	−824.2 kJ/mol
Gibbs free energy (ΔfG⦵)	−742.2 kJ/mol
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P305+P351+P338
NFPA 704 (fire diamond)	0 0 0
Threshold limit value (TLV)	5 mg/m3 (TWA)
	Lethal dose or concentration (LD, LC):
LD50 (median dose)	10 g/kg (rats, oral)
	NIOSH (US health exposure limits):
PEL (Permissible)	TWA 10 mg/m3
REL (Recommended)	TWA 5 mg/m3
IDLH (Immediate danger)	2500 mg/m3
Related compounds
Other anions	Iron(III) fluoride
Other cations	Manganese(III) oxide; Cobalt(III) oxide
Related iron oxides	Iron(II) oxide; Iron(II,III) oxide
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe₂O₃. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe₃O₄), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe₂O₃ is the main source of iron for the steel industry. Fe₂O₃ is readily attacked by acids. Iron(III) oxide is often called rust, since rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as hydrous ferric oxide.

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