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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
System:IsometricColour:Black
Hardness:5½
Member of:Spinel Group
Name:In allusion to the composition, containing MAGNESIum and its relationship to CHROMITE.


Spinel Group, Cr subgroup. Chromite-Magnesiochromite Series and Magnesiochromite-Spinel Series. It apparently 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.

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

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:Metallic
Colour:Black
Hardness (Mohs):5½
Tenacity:Brittle
Cleavage:None Observed
Fracture:Irregular/Uneven
Density (measured):4.1 - 4.3 g/cm3
Density (calculated):4.43 g/cm3

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 rare, octahedral, modified by {001} at times. Massive.

Optical Data of Magnesiochromite

Type:Isotropic

Chemical Properties of Magnesiochromite

Formula:
Mg(Cr,Al,Fe)
 
2
O
 
4
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:

- +
Chromite
Fe(Cr,Al,Fe)
 
2
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
Magnesioferrite
MgFe
3+
2
O
 
4
Magnetite
Fe
2+
 
Fe
3+
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
Related Minerals - Nickel-Strunz Grouping):

- +
4.BB.05Brunogeierite
(Ge,Fe)Fe
 
2
O
 
4
4.BB.05Chromite
Fe(Cr,Al,Fe)
 
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
 
x
([Cr,Fe,V]
3+
2x
Ti
 
8-2x
)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(Cr,Al,Fe)
 
2
O
 
4
7.14.14 Donathite

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:镁铬铁矿
Spanish:Magnesiochromita
Mitchellita
Varieties:
Alumo-chrompicotitePicrochromite

Other Information

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:

- +
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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