Petrogenetic implication of the Mössbauer hyperfine parameters of Fe<sup>3+</sup>-chromites from Sukinda (India) ultramafites

Mitra, S.

doi:10.1180/minmag.1991.055.381.06

Cited by 20 publications

(4 citation statements)

References 23 publications

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“…Spectra at intermediate temperatures were collected to clarify the unexpected temperature dependence of the isomer shift and area ratio 9 CR5 spinel produced spectra (Fig. 2) similar to those already reported for lherzolite and Cr-bearing spinels (Wood and Virgo, 1989;Mitra et al, 1991;Osborne et al, 1981). In the R.T. spectrum, three well-resolved absorption peaks were evident; moreover, the high-velocity peak clearly derived from the overlap of two smaller ones.…”

Section: Methodssupporting

confidence: 54%

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

1996

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Three natural spinels of different places of occurrence and compositions were investigated by means of microprobe chemical analysis, single crystal X-ray diffraction and MOssbauer spectroscopy. All cation distributions between T and M sites were calculated from microprobe and XRD experimental data, by means of a mathematical model with appropriate assumptions. Fe 2 § and Fe 3 § assignments calculated in this way were compared with those observed in MOssbauer spectra. The satisfactory agreement found proves, at least in the samples studied, the reliability of the model and the assumptions used. In the spinels examined, such results show Fe 2 § and Fe 3 § virtually ordered in T and M sites respectively. M6ssbauer data also revealed Fe 2 § in different tetrahedral sites due to the next-nearest neighbour effect, probably as a consequence of spinel genetic conditions.

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Section: Methodssupporting

confidence: 54%

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

1996

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“…We propose that this oxidation was post-magmatic. Similar highly oxidized chromites have been described from chromitites associated with Proterozoic ultramafic rocks in the Sukinda area of eastern India (Mitra et al, 1991). One mechanism by which oxidation of spinels may take place is through in situ heating (Menegazzo et al, 1997;Martignago et al, 2003).…”

Section: The High Fe 3+ /Sfe Ratio Groupsupporting

confidence: 66%

“…Electrons released are then localized in the octahedral B sites, reducing Fe 3+ to Fe 2+ . The model was used by Mitra et al (1991) to fit spectra of Cr-spinel samples with similar high-Fe 3+ compositions to those found in Cr 03-11 and Cr 04-11.…”

Section: Modelmentioning

confidence: 99%

New Mössbauer measurements of Fe³⁺/ΣFe in chromites from the mantle section of the Oman ophiolite: evidence for the oxidation of the sub-oceanic mantle

Rollinson¹,

Adetunji²,

Yousif³

et al. 2012

Mineral. mag.

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Room temperature Mössbauer and electron-probe measurements of Fe3+/ΣFe in chromite from the mantle section of the Oman ophiolite define two groups of samples: a low Fe3+/ΣFe group (with Fe3+/ΣFe = 0.21–0.36) have cr# = Cr/(Cr + Al) in the range 0.49–0.75, whereas a smaller more geographically localized high Fe3+/ΣFe group (with Fe3+/ΣFe = 0.71–0.78) have a more restricted range of cr# ratios of 0.72–0.75. The low Fe3+/ΣFe chromitites have very variable Fe3+/ΣFe ratios. They are thought to have crystallized from melts that have interacted with depleted mantle and thereby acquired their variable Fe3+/ΣFe ratio. The high Fe3+/ΣFe chromitites are restricted to one small area of the mantle and their high oxidation state is thought to be post magmatic. They are either the product of later heating, related to melt flux or interaction with a later oxidising melt. A difference in oxygen fugacity between the MORB-depleted harzburgite host, which is at the quartz–fayalite–magnetite (QFM) buffer and the later chromite-bearing melts (QFM + 2) implies that there is a real difference in the oxidation state of the MORB and arc-magma sources.

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“…These anomalies are not unique, but somewhat similar trends have been observed by Lodya et al (1994) in natural chromite from the Bushveld Complex in South Africa. They suggested that this is due to a structural phase transition which they found evident from the broadening of the M/Sssbauer linewidth at approximately the same temperature (Lodya et al, 1994;Mitra et al, 1991;Fatseas et al, 1976). Indeed, our specimens did show a broadening of the MOssbauer spectrum between 77 and 298 K (A1-Alawi et al, 1996), but whether this starts occurring at 160 K requires a more scrupulous investigation.…”

supporting

confidence: 47%

Magnetic susceptibilities of chromites from Oman

et al. 1997

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MINERALOGICAL and physical characteristics of natural chromites from Oman ophiolites have been recently investigated using M6ssbauer spectrocopy (MS), X-ray diffraction (XRD) and Scanning electron microscopy (SEM) by Al-Alawi et al. (1996). From the MS analysis together with the SEM data, they derived the chemical formula for specimens collected from two separate chromite deposits named Tawiyah (15 km NNW of Nakhal) and Khobar (on the Luzugh-Semail road) and proposed respectively as follows: F2+ ,, 2+ ~ 3+ ~ 3+ --,3+ ~2-eo.291Vlgo.71 l"eo. 12Lro.99Ptlo.s9U4 and F2+ r~,~ 2+ ~ 3+ c, 3+ A13+ r',.2-eo. 141vlgo.8ol~ eo.o9~r 1.o3 ,~10.93v4Furthermore, their MS data reveal that the ferrous/ferric ratio remains constant at different temperatures which suggests an ordered distribution of the cations. The aims of this work are to characterize further the specimens of natural chromite from Tawiyah and Khobar and to investigate their magnetic properties taking into account the results of the earlier study.First, the raw powdered samples were sieved to eliminate the fine fraction and retain grains with size larger than 335 mm. Then they were passed through a magnetic separator in order to remove the gangue from the pure chromite. Finally, they were examined under the binocular microscope up to 100x magnification showing the dark chromite grains and the remaining clear gangue grains. This separation process was repeated as often as necessary until no observable impurities remained. The X-ray measurements revealed that some traces of Ti and Mn (< 0.01%) were present but have been neglected in establishing the chemical formulae.The magnetic susceptibility measurements were performed using a Faraday analytical microbalance of 1 I~g precision. An electromagnet with specially shaped poles for constant field gradient, produced field strengths of 4, 5 and 6 kOe. The magnet was calibrated with Mohr's salt having a susceptibility of 32.32 x 10 -6 emu g-1 at 20~ During the experiment, the sample was contained in a quartz bucket having a temperature independent diamagnetism over a wide range which could be substracted from the measured magnetic force. An Oxford liquid nitrogen cryostat provided with a heater enabled scanning the temperatures between 77 and 500 K.The data of the mass magnetic susceptibility ~m inverse versus temperature T are shown in Fig. 1. As can be seen, the Khobar specimen data are magnetic field dependent especially in the middle range, most probably because of some remaining magnetic impurities. In order to extract the purely paramagnetic contribution, we then had to extrapolate to infinite field (1/H~0) as shown in the figure. The Tawiyah specimen data are field independent. The order of magnitudes of ~m confirms well the paramagnetism detected by the MS spectra of AIAlawi et al. (1996) for both specimens down to 77 K.However, it is difficult to determine the magnetic transition temperature by extrapolation since our lowest point is certainly above the known measured N6el temperature of 75 K (Murad and Johns...

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Petrogenetic implication of the Mössbauer hyperfine parameters of Fe³⁺-chromites from Sukinda (India) ultramafites

Cited by 20 publications

References 23 publications

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

New Mössbauer measurements of Fe³⁺/ΣFe in chromites from the mantle section of the Oman ophiolite: evidence for the oxidation of the sub-oceanic mantle

Magnetic susceptibilities of chromites from Oman

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Petrogenetic implication of the Mössbauer hyperfine parameters of Fe3+-chromites from Sukinda (India) ultramafites

Cited by 20 publications

References 23 publications

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

Cation distribution in some natural spinels from X-ray diffraction and Mössbauer spectroscopy

New Mössbauer measurements of Fe3+/ΣFe in chromites from the mantle section of the Oman ophiolite: evidence for the oxidation of the sub-oceanic mantle

Magnetic susceptibilities of chromites from Oman

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Petrogenetic implication of the Mössbauer hyperfine parameters of Fe³⁺-chromites from Sukinda (India) ultramafites

New Mössbauer measurements of Fe³⁺/ΣFe in chromites from the mantle section of the Oman ophiolite: evidence for the oxidation of the sub-oceanic mantle