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Magnesiochromite

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Delight Quarry (Soldier's Delight Quarry; Dyer Quarry), Soldiers' Delight ridge, Delight, Baltimore Co., Maryland, USA
© 2009, JGW

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Formula:
Mg(Cr,Al,Fe)
 
2
O
 
4
Mg may be partially replaced by divalent Fe.
System:IsometricColour:Black, deep red
Hardness:5½
Member of:Spinel Group
Name:Named by Antoine François Alfred Lacroix in 1910 in allusion to the composition, containing MAGNESIum and its relationship to CHROMITE. The mineral was originally named magnochromite by G. M. von Bock in 1868.
Isostructural with:Chromite, Magnetite


Spinel Group, Cr subgroup. Chromite-Magnesiochromite Series and Magnesiochromite-Spinel Series. It forms a complete solid solution series with many other members of the group. It is the magnesium analogue of zincochromite, cochromite, manganochromite and chromite and the Cr analogue of spinel and magnesioferrite.

It usually contains ferrous iron [Fe(II)], ferric iron [Fe(III)], and Al. "Ferritchromite", i.e. Fe(III) substitutions for Al and Cr, usually in grain rims, may give high total Fe and a false chromite identification, whereas Fe(II)> Mg is the actual deciding factor in the species designation for chromite. Magnesiochomite is about twice as common as chromite.

Much of the mineral referred to as "chromite" in geological and petrological papers and mining statistics is magnesiochromite. The Fe-dominant species chromite may be subordinate to magnesiochromite in many "chromite" deposits, chromitites, and other "chromite"-bearing rocks.

Note: Chromite, that is near end-member, has a higher specific gravity than near end-member magnesiochromite.

Classification of Magnesiochromite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:4/B.03-10
Nickel-Strunz 10th (pending) edition ID:4.BB.05

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
B : Metal: Oxygen = 3:4 and similar
B : With only medium-sized cations
Dana 8th edition ID:7.2.3.1

7 : MULTIPLE OXIDES
2 : AB2X4
Hey's CIM Ref.:7.14.13

7 : Oxides and Hydroxides
14 : Oxides of Cr
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Type Occurrence of Magnesiochromite

Type Locality:Schwarzenberg District, Erzgebirge, Saxony, Germany
Year of Discovery:1868

Physical Properties of Magnesiochromite

Lustre:Greasy, Metallic, Sub-Metallic
Diaphaneity (Transparency):Opaque
Colour:Black, deep red
Streak:Brown
Hardness (Mohs):5½
Tenacity:Brittle
Cleavage:None Observed
Parting:Parting may be present on {111}
Fracture:Irregular/Uneven, Hackly, Sub-Conchoidal
Comment:Broken surfaces may have an angular granulated appearance
Density (measured):4.1 - 4.3 g/cm3
Density (calculated):4.43 g/cm3
Comment:Large crystals of "chomite" may be distinguished by specific gravity.

Crystallography of Magnesiochromite

Crystal System:Isometric
Class (H-M):m3m (4/m 3 2/m) - Hexoctahedral
Space Group:Fd3m {F41/d 3 2/m}
Cell Parameters:a = 8.305Å
Unit Cell Volume:V 572.82 ų (Calculated from Unit Cell)
Morphology:Crystals may be octahedral, sometimes modified by {001}, etc. Commonly massive.
X-Ray Powder Diffraction:
d-spacingIntensity
4.81 (60)
2.95 (10)
2.51 (100)
2.08 (50)
1.60 (40)
1.47 (50)
1.41 (10)
Comments:ICDD 10-351 (synthetic)

Optical Data of Magnesiochromite

Type:Isotropic
Type:Isotropic
Pleochroism:Non-pleochroic

Chemical Properties of Magnesiochromite

Formula:
Mg(Cr,Al,Fe)
 
2
O
 
4


Mg may be partially replaced by divalent Fe.
Essential elements:Cr, Mg, O
All elements listed in formula:Al, Cr, Fe, Mg, O
Common Impurities:Fe,Al

Relationship of Magnesiochromite to other Species

Series:Forms a series with Spinel (see here)
Forms a series with Chromite (see here)
Member of:Spinel Group
Other Members of Group:

- +
Brunogeierite
Fe
2+
2
Ge
4+
 
O
 
4
Chromite
Fe
2+
 
Cr
3+
2
O
 
4
Cochromite
(Co,Ni,Fe)(Cr,Al)
 
2
O
 
4
Coulsonite
Fe
2+
 
V
3+
2
O
 
4
Cuprospinel
Cu
2+
 
Fe
3+
2
O
 
4
Filipstadite
(Mn,Mg)
 
2
(Sb
 
.5
Fe
 
.5
)O
 
4
Franklinite
Zn
2+
 
Fe
3+
2
O
 
4
Gahnite
ZnAl
 
2
O
 
4
Galaxite
(Mn,Fe,Mg)(Al,Fe)
 
2
O
 
4
Hercynite
Fe
2+
 
Al
 
2
O
 
4
Jacobsite
Mn
2+
 
Fe
3+
2
O
 
4
Magnesiocoulsonite
MgV
 
2
O
 
4
Magnesioferrite
MgFe
3+
2
O
 
4
Magnetite
Fe
2+
 
Fe
3+
2
O
 
4
Manganochromite
(Mn,Fe)(Cr,V)
 
2
O
 
4
Nichromite
(Ni,Co,Fe)(Cr,Fe,Al)
 
2
O
 
4
Qandilite
(Mg,Fe)
 
2
(Ti,Fe,Al)O
 
4
Spinel
MgAl
 
2
O
 
4
Trevorite
Ni
2+
 
Fe
3+
2
O
 
4
Ulvöspinel
Fe
 
2
TiO
 
4
Vuorelainenite
(Mn,Fe)(V,Cr)
 
2
O
 
4
Zincochromite
ZnCr
 
2
O
 
4
Related Minerals - Nickel-Strunz Grouping):

- +
4.BB.05Brunogeierite
Fe
2+
2
Ge
4+
 
O
 
4
4.BB.05Chromite
Fe
2+
 
Cr
3+
2
O
 
4
4.BB.05Cochromite
(Co,Ni,Fe)(Cr,Al)
 
2
O
 
4
4.BB.05Coulsonite
Fe
2+
 
V
3+
2
O
 
4
4.BB.05Cuprospinel
Cu
2+
 
Fe
3+
2
O
 
4
4.BB.05Filipstadite
(Mn,Mg)
 
2
(Sb
 
.5
Fe
 
.5
)O
 
4
4.BB.05Franklinite
Zn
2+
 
Fe
3+
2
O
 
4
4.BB.05Gahnite
ZnAl
 
2
O
 
4
4.BB.05Galaxite
(Mn,Fe,Mg)(Al,Fe)
 
2
O
 
4
4.BB.05Hercynite
Fe
2+
 
Al
 
2
O
 
4
4.BB.05Jacobsite
Mn
2+
 
Fe
3+
2
O
 
4
4.BB.05Manganochromite
(Mn,Fe)(Cr,V)
 
2
O
 
4
4.BB.05Magnesiocoulsonite
MgV
 
2
O
 
4
4.BB.05Magnesioferrite
MgFe
3+
2
O
 
4
4.BB.05Magnetite
Fe
2+
 
Fe
3+
2
O
 
4
4.BB.05Nichromite
(Ni,Co,Fe)(Cr,Fe,Al)
 
2
O
 
4
4.BB.05Qandilite
(Mg,Fe)
 
2
(Ti,Fe,Al)O
 
4
4.BB.05Spinel
MgAl
 
2
O
 
4
4.BB.05Trevorite
Ni
2+
 
Fe
3+
2
O
 
4
4.BB.05Ulvöspinel
Fe
 
2
TiO
 
4
4.BB.05Vuorelainenite
(Mn,Fe)(V,Cr)
 
2
O
 
4
4.BB.05Zincochromite
ZnCr
 
2
O
 
4
4.BB.10Hausmannite
MnMn
 
2
O
 
4
4.BB.10Hetaerolite
ZnMn
 
2
O
 
4
4.BB.10Hydrohetaerolite
ZnMn
 
2
O
 
4
 · H
 
2
O
4.BB.10Iwakiite
Mn(Fe,Mn)
 
2
O
 
4
4.BB.15Maghemite
Fe
3+
2
O
 
3
4.BB.15Titanomaghemite
Fe
3+
 
(Fe
3+
 
,Ti
4+
 
,Fe
2+
 
,◻)
 
2
O
 
4
4.BB.20Tegengrenite
(Mg,Mn
2+
 
)
 
2
Sb
5+
0.5
(Mn
3+
 
,Si,Ti)
 
0.5
O
 
4
4.BB.25Xieite
Fe
2+
 
Cr
 
2
O
 
4
Related Minerals - Hey's Index Grouping:

- +
7.14.1Eskolaite
Cr
 
2
O
 
3
7.14.2Bracewellite
CrO(OH)
7.14.3Grimaldiite
CrO(OH)
7.14.4Guyanaite
CrO(OH)
7.14.5Yimengite
K(Cr,Ti,Fe,Mg)
 
12
O
 
19
7.14.6Mathiasite
K(Ti,Cr,Fe,Mg,Zr)
 
21
O
 
38
7.14.7Mcconnellite
CuCrO
 
2
7.14.8Redledgeite
Ba(Ti
4+
6
Cr
3+
2
)O
 
16
7.14.9Hawthorneite
Ba(MgTi
 
3
Cr
 
4
Fe
 
4
)O
 
19
7.14.10Zincochromite
ZnCr
 
2
O
 
4
7.14.11Wattersite
(Hg
+
2
)
 
2
Hg
2+
 
(CrO
 
4
)O
 
2
7.14.12Chromite
Fe
2+
 
Cr
3+
2
O
 
4

Other Names for Magnesiochromite

Synonyms:
Chrome-Spinel (of Boldyrev)FerrichromspinelMagnesiochromite (of Bock)Magnesiochromite (of Simpson)Magnochromite (of Fisher)
Mitchellite
Other Languages:
German:Magnesiochromit
Mitchellit
Japanese:苦土クロム石
Russian:Магнезиохромит
Simplified Chinese:镁铬尖晶石
镁铬铁矿
Spanish:Magnesiochromita
Mitchellita
Varieties:
Alumo-chrompicotitePicrochromite

Other Information

Fluorescence in UV light:Not fluorescent in UV
Special Storage/
Display Requirements from:
Tumet river, Asosa region, Benshangul-Gumaz Province, EthiopiaRounded monograins up to 6 cm in diameter.
Health Warning:No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Magnesiochromite

Reference List:

- +
von Bock, G. M. (1868) Inaugual Dissertation, Beslau.

Websky, W. (1873) Zeitschrift Deutchland Geol. Gesselschaft, 25:394.

Dana, System of Mineralogy, Sixth ed. (1892): 228.

Simpson (1920), Mineralogical Magazine: 19: 99 (as Picrochromite).

Fisher (1929), American Mineralogist: 14: 355 (as Magnochromite).

Betekhtin (1934), Ann. Inst. Mines, Leningrad: 8: 38 (as Ferrichromsinel).

Palache, Charles, Harry Berman & Clifford Frondel (1944), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume I: Elements, Sulfides, Sulfosalts, Oxides. John Wiley and Sons, Inc., New York. 7th edition, revised and enlarged: 709-712.

Canadian Mineralogist (1994): 32: 729-746.

O'Neill, H.St.C. and Dollase, W.A. (1994) Crystal structures and cation distribution in simple spinels from powder XRD structural refinements: MgCr2O4, ZnCr2O4, Fe3O4, and the temperature dependence of the cation distribution in ZnAl2O4. Physics and Chemistry of Minerals: 20: 541-555.

Internet Links for Magnesiochromite

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  • Raman and XRD data at RRUFF project
  • American Mineralogist Crystal Structure Database
  • Magnesiochromite details from Handbook of Mineralogy (PDF)
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