Chromium(III) oxide

Chromium(III) oxide

Names
Other names Chromium sesquioxide Chromia Chrome green Eskolaite
Identifiers
CAS Number	1308-38-9 Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:48242 Y
ChemSpider	451305 Y
ECHA InfoCard	100.013.783
PubChem	517277
RTECS number	GB6475000
UNII	X5Z09SU859 Y
InChI InChI=1S/2Cr.3O Y Key: QDOXWKRWXJOMAK-UHFFFAOYSA-N Y InChI=1/2Cr.3O/rCr2O3/c3-1-5-2-4 Key: QDOXWKRWXJOMAK-LUXALHLMAR
SMILES O=[Cr]O[Cr]=O
Properties
Chemical formula	Cr2O3
Molar mass	151.9904 g/mol
Appearance	light to dark green, fine crystals
Density	5.22 g/cm3
Melting point	2,435 °C (4,415 °F; 2,708 K)
Boiling point	4,000 °C (7,230 °F; 4,270 K)
Solubility in water	insoluble
Solubility in alcohol	insoluble in alcohol, acetone, acids
Magnetic susceptibility (χ)	+1960.0·10−6 cm3/mol
Refractive index (nD)	2.551
Structure
Crystal structure	hexagonal
Thermochemistry
Std molar entropy (So298)	81 J·mol−1·K−1
Std enthalpy of formation (ΔfHo298)	−1128 kJ·mol−1
Hazards
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 1 mg/m3
REL (Recommended)	TWA 0.5 mg/m3
IDLH (Immediate danger)	250 mg/m3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

Chromium(III) oxide is the inorganic compound of the formula Cr
2O
3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

Cr
2O
3 adopts the corundum structure, consisting of a hexagonal close packed array of oxide anions with ⅔ of the octahedral holes occupied by chromium. Similar to corundum, Cr
2O
3 is a hard, brittle material (Mohs hardness 8 to 8.5). It is antiferromagnetic up to 307 K, the Néel temperature. It is not readily attacked by acids or bases, although molten alkali gives chromate salts with the CrO−
4 anion. It turns brown when heated, but reverts to its dark green color when cooled. It is also hygroscopic.

Cr
2O
3 occurs naturally in mineral eskolaite, which is found in chromium-rich tremolite skarns, metaquartzites, and chlorite veins. Eskolaite is also a rare component of chondrite meteorites. The mineral is named after Finnish geologist Pentti Eskola.