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Luogufengite; a new nano-mineral of Fe (sub 2) O (sub 3) polymorph with giant coercive field

Huifang Xu, Seungyeol Lee and Hongwu Xu
Luogufengite; a new nano-mineral of Fe (sub 2) O (sub 3) polymorph with giant coercive field
American Mineralogist (April 2017) 102 (4): 711-719


Luogufengite, Al-bearing epsilon -Fe (sub 2) O (sub 3) , is a new member of Fe (sub 2) O (sub 3) polymorphs discovered in late Pleistocene basaltic scoria from the Menan Volcanic Complex nearby Rexburg, Idaho. It is an oxidation product of Fe-bearing basaltic glass at high temperature and is associated with maghemite and hematite. Luogufengite is an euhedral or semi-euhedral nano-mineral with its crystal size ranging from approximately 20 to approximately 120 nm. The mineral has a space group of Pna2 (sub 1) ; its unit-cell parameters refined from synchrotron X-ray powder diffraction pattern are a = 5.0647(3), b = 8.7131(6), c = 9.3842(5) A, and Z = 4 (calculated density = 4.905 g/cm (super 3) ) with the doubled hexagonal (ABAC) packing of oxygen atoms. The eight strongest lines of the measured X-ray diffraction pattern [d(A)(I)(hkl)] are: 3.197(27.3)(022); 2.945(29.1) (013); 2.708(100)(122); 2.437(35.8)(131); 1.716(24.4)(204); 1.507(40.7)(135); and 1.458(37.2)(330). The empirical formula is Fe (sub 1.71) Al (sub 0.24) Mg (sub 0.02) Ti (sub 0.03) O (sub 3) . The crystals display (110) twins with twin boundaries of (110), (100), and (130) due to their pseudo-hexagonal symmetry. Luogufengite is an important mineral that records paleomagnetism of volcanic rocks because of its large magnetic coercivity. This unique magnetic property of the mineral may explain the observed unusually high-remanent magnetization in some igneous and metamorphic rocks and even martian rocks with high-remanent magnetization. Some intergrowths of magnetite with ilmenite exsolution lamellae or hematite with magnetite lamellar precipitates have luogufengite-like 2D crystalline characteristics with the doubled hexagonal packing at the interface between cubic and rhombohedral structures. Luogufengite-like nano-domains at the magnetite/hematite interfaces might be responsible for the large coercive field of lodestones that are partially oxidized magnetite with hematite micro-precipitates.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 102
Serial Issue: 4
Title: Luogufengite; a new nano-mineral of Fe (sub 2) O (sub 3) polymorph with giant coercive field
Affiliation: University of Wisconsin at Madison, Department of Geoscience, Madison, WI, United States
Pages: 711-719
Published: 201704
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 37
Accession Number: 2017-041504
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
N43°37'00" - N43°55'60", W112°00'00" - W111°24'00"
Secondary Affiliation: Los Alamos National Laboratory, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201723
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