IMA 2016-005 = luogufengite

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Marco E. Ciriotti
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IMA 2016-005 = luogufengite

Messaggio da Marco E. Ciriotti » ven 02 dic, 2016 9:28

Prossima pubblicazione.

Referenza:
▪ Xu, Hu., Lee, S., Xu, H. (2017): Luogufengite: A new nano-mineral of Fe2O3 polymorph with giant coercive field. American Mineralogist, 102, (in press).

N.d.R.: a nano-crystals (~20 - ~150 nm) polymorph of hematite.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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Re: IMA 2016-005 = luogufengite

Messaggio da Marco E. Ciriotti » gio 30 mar, 2017 10:36

Pubblicazione effettuata.

Referenza:
▪ Xu, H., Lee, S., Xu, H. (2017): Luogufengite: A new nano-mineral of Fe2O3 polymorph with giant coercive field. American Mineralogist, 102, 711-719.

Abstract:
Luogufengite, Al-bearing e-Fe2O3, is a new member of Fe2O3 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 ~20 to ~120 nm. The mineral has a space group of Pna21; 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) Å, and Z = 4 (calculated density = 4.905 g/cm3) with the doubled hexagonal (ABAC) packing of oxygen atoms. The eight strongest lines of the measured X‑ray diffraction pattern [d(Å)(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 Fe1.71Al0.24Mg0.02Ti0.03O3. 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.
Marco E. Ciriotti

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Marco E. Ciriotti
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Re: IMA 2016-005 = luogufengite

Messaggio da Marco E. Ciriotti » mer 11 apr, 2018 12:28

Referenza:
▪ Lee, S. & Xu, H. (2018): The Role of ε-Fe2O3 Nano-Mineral and Domains in Enhancing Magnetic Coercivity: Implications for the Natural Remanent Magnetization. Minerals, 8, 97; doi:10.3390/min8030097.

Abstract:
A natural ε-Fe2O3 nano-mineral (luogufengite) has been discovered in young basaltic rocks around the world. Transmission electron microscopy (TEM) observed euhedral or subhedral luogufengite nano-minerals with crystal sizes ranging from 10 to 120 nm in the basaltic rocks. The magnetic property of treated scoria sample (containing 75.3(5) wt % luogufengite) showed a saturation remanence of 11.3 emug􀀀1 with a coercive field of 0.17 tesla (T) at room temperature. Luogufengite-like nano-domains were also observed in natural permanent magnets (lodestone) and Fe-Ti oxides (ilmenite-magnetite series) with strong remanent magnetization. The structure of luogufengite-like domains (double hexagonal close-packing) is associated with the interfaces between the (111) plane of cubic magnetite and the (0001) plane of rhombohedral hematite or ilmenite. Stacking faults and twin boundaries of magnetite/maghemite can also produce the luogufengite-like domains. The nano-domains oriented along the magnetic easy axis play an essential role in enhancing the magnetic coercivity of lodestone and Fe-Ti oxide. We conclude that the luogufengite nano-minerals and nano-domains provide an explanation for coercivity and strong remanent magnetization in igneous, metamorphic rocks and even some reported Martian rocks. These nano-scaled multilayer structures extend our knowledge of magnetism and help us to understand the diverse magnetic anomalies occurring on Earth and other planetary bodies.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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