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, acetic acid
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 occurs in nature as the mineral hematite, which serves as the primary source of iron for the steel industry. It is also known as red iron oxide, especially when used in pigments.

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.

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.

Ferric oxide is readily attacked by even weak acids. It is a weak oxidising agent, most famously when reduced by aluminium in the thermite reaction.