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Xieite

Formula:
Fe
2+
 
Cr
 
2
O
 
4
System:Orthorhombic
Dimorph of:Chromite


Spinel group. High pressure polymorph of chromite.
Abstract (from Chen, et al, 2003): The first natural occurrence of a high-pressure polymorph of chromite has been discovered in the shock-metamorphosed Suizhou meteorite. The composition of this high-pressure polymorph is identical to that of the precursor chromite. The Raman spectrum of this polymorph is distinct from that of chromite. Synchrotron X-ray diffraction analysis revealed that this polymorph has an orthorhombic CaTi2O4-type structure. The cell parameters are: a = 9.462(6) Å, b = 9.562(9) Å, c = 2.916(1) Å, V = 263.8(4) Å3 (Z=4), space group = Bbmm, and the density = 5.63 g/cm3 (the numbers in parentheses are standard deviations on the last significant digits). This polymorph is 11.5% denser than chromite. The P-T conditions for the phase transformation from chromite to the CaTi2O4-structured polymorph are estimated at 20–23 GPa and 1800 to 2000 °C, respectively. This dense CaTi2O4-structured FeCr2O4 phase could be a host phase for Cr, Al, Fe, Mg and Mn and other metallic elements in the deep Earth.

Classification of Xieite

IMA status:Approved 2007
Nickel-Strunz 10th (pending) edition ID:4.B0.

4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
B : Metal: Oxygen = 3:4 and similar
0 :
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Type Occurrence of Xieite

Type Locality:Suizhou meteorite (Suizhou L6 chondrite), Dayanpo, Zengdu District, Suizhou Prefecture, Hubei Province, China
Geological Setting of type material:L6 chondrite meteorite

Crystallography of Xieite

Crystal System:Orthorhombic
Cell Parameters:a = 9.462Å, b = 9.562Å, c = 2.916Å
Ratio:a:b:c = 0.99 : 1 : 0.305
Unit Cell Volume:V 263.83 ų (Calculated from Unit Cell)

Chemical Properties of Xieite

Formula:
Fe
2+
 
Cr
 
2
O
 
4
Essential elements:
All elements listed in formula:Cr, Fe, O
Empirical Formula:
Fe
2+
 
Cr
 
2
O
 
4

Other Names for Xieite

Synonyms:
IMA2007-056
Simplified Chinese names:
谢氏超晶石

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 Xieite

Reference List:Chen, M., Shu, J., Xie, X., Mao, H. (2003): Natural CaTi2O4-structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta, 67, 3937-3942.

Chen, M., Shu, J., Mao, H., Xie, X., Hemley, R.J. (2003): Natural occurrence and synthesis of two new postspinel polymorphs of chromite. Proceedings of the National Academy of Science USA, 100, 14651-14654.

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    Localities for Xieite

    (TL) indicates type locality. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
    China
     
    • Hubei Province
      • Suizhou Prefecture
        • Zengdu District
          • Dayanpo
    Chen, M., Shu, J., Xie, X., Mao, H. (2003): Natural CaTi2O4-structured FeCr2O4 polymorph in the Suizhou meteorite and its significance in mantle mineralogy. Geochimica et Cosmochimica Acta, 67, 3937-3942; IMA website
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