The mechanism of exsolution of hematite from iron-bearing rutile

Putnis, Andrew

doi:10.1007/bf00308121

Cited by 31 publications

(24 citation statements)

References 11 publications

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“…The resulting relationship is thus thermodynamically driven and differs from case to case. This type of relationships is best described by OR-2, which roughly corresponds to all rutile/hematite intergrowths in natural samples (Armbruster 1981;Daneu et al 2007Daneu et al , 2014 and exsolutions of hematite in rutile (Putnis 1978) with small but important deviations that can serve as a precise geothermometer (Banfield and Veblen 1991;Hwang et al 2010). In the case of rutile exsolutions form Mwinilunga, we showed that rutile and hematite roughly obey the OR-2 law with 0.59° angular deviation, producing a new OR-3 relationship.…”

Section: Discussionmentioning

confidence: 97%

“…On the other hand, when exsolution is slow, the daughter phase has ample time to establish an equilibrium interface with the parent phase. Under such nucleation conditions, rutile chooses the best matching interface that produces the lowest free energy with hematite under given p − T conditions (Putnis 1978(Putnis , 1992. As a consequence, topotaxial growth of rutile is controlled by structural coherency between hematite and rutile at the time of its exsolution.…”

Section: Discussionmentioning

confidence: 99%

“…9). The mechanism of hematite exsolution from Fe-bearing rutile was thoroughly studied by Putnis (1978) in the temperature range between 475 and 600 °C. He showed that transformation passes through an intermediate Fe-rich phase possessing high structural coherency with the rutile structure and is characterized by tripling of the rutile's {101} diffraction spots associated with Fe distribution.…”

Section: Discussionmentioning

confidence: 99%

“…TEM investigations of hematite exsolution from Fe-rich rutile have shown that their OR strongly depends on the formation conditions (Putnis 1978). Minimization of interfacial energy at the given formation condition was proposed as the main mechanism for establishing a particular OR (Hwang et al 2010) and could be held responsible for different ORs that were observed on rutile/hematite intergrowths (Armbruster 1981).…”

Section: Introductionmentioning

confidence: 99%

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Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Rečnik

Stanković

Daneu

2015

Contrib Mineral Petrol

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samples. Using a HRTEM and high-angle annular dark-field scanning TEM methods combined with energy-dispersive X-ray spectroscopy, we identified remnants of ilmenite lamellae in the vicinity of rutile exsolutions, which were an important indication of the high-T formation of the primary ferrian-ilmenite crystals. Another type of exsolution process was observed in rutile crystals, where hematite precipitates topotaxially exsolved from Fe-rich parts of rutile through intermediate Guinier-Preston zones, characterized by tripling the {101} rutile reflections. Unlike rutile exsolutions in hematite, hematite exsolutions in rutile form {301} R |{030} H equilibrium interfaces. The overall composition of our samples indicates that the ratio between ilmenite and hematite in parent ferrianilmenite crystals was close to Ilm 67 Hem 33 , typical for Fe-Tirich differentiates of mafic magma. The presence of ilmenite lamellae indicates that the primary solid solution passed the miscibility gap at ~900 °C. Subsequent exsolution processes were triggered by surface oxidation of ferrous iron and remobilization of cations within the common oxygen sublattice. Based on nanostructural analysis of the samples, we identified three successive exsolution processes: (1) exsolution of ilmenite lamellae from the primary ferrian-ilmenite crystals, (2) exsolution of rutile lamellae from ilmenite and (3) exsolution of hematite precipitates from Fe-rich rutile lamellae. All observed topotaxial reactions appear to be a combined function of temperature and oxygen fugacity, fO 2 .Keywords Ilmenite · Hematite · Rutile · Topotaxy · Exsolution · Intergrowth · Geothermometer IntroductionVarious intergrowths of rutile with structurally related minerals are known in nature. They are found in igneous and Abstract Oriented rutile/hematite intergrowths from Mwinilunga in Zambia were investigated by electron microscopy methods in order to resolve the complex sequence of topotaxial reactions. The specimens are composed of up to several-centimeter-large euhedral hematite crystals covered by epitaxially grown reticulated rutile networks. Following a top-down analytical approach, the samples were studied from their macroscopic crystallographic features down to subnanometer-scale analysis of phase compositions and occurring interfaces. Already, a simple morphological analysis indicates that rutile and hematite are met near the �010� R {101} R ||�001� H {110} H orientation relationship. However, a more detailed structural analysis of rutile/hematite interfaces using electron diffraction and high-resolution transmission electron microscopy (HRTEM) has shown that the actual relationship between the rutile and hosting hematite is in fact �010� R {401} R ||�001� H {170} H . The intergrowth is dictated by the formation of {170} H |{401} R equilibrium interfaces leading to 12 possible directions of rutile exsolution within a hematite matrix and 144 different incidences between the intergrown rutile crystals. Analyzing the potential rutile-rutile interfaces, these could be ...

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Rečnik

Stanković

Daneu

2015

Contrib Mineral Petrol

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“…according to the reviews by E1 Goresy (1976b), Rumble (1976), Frost (1991), Haggerty (1991) and Deer et al (1992, p. 548-51). Putnis (1978) and Pinet and Smith (1985) recognized hematite exsolution from futile, and Smith (1988) suggested corundum exsolution. The divalent transition element cation Ni 2+ was recorded by Smith and Pinet (1985) but apparently no one has ever detected Co 2+.…”

Section: Ion Substitutions In the Rutile Structurementioning

confidence: 99%

Sb-rich rutile in the manganese concentrations at St. Marcel-Praborna, Aosta Valley, Italy: petrology and crystal-chemistry

Smith

Perseil

1997

Mineral. mag.

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The petrographical, crystal-chemical and petrogenetical aspects of rutile rich in antimony (up to 33.75 wt.% Sb205; equal to 0.2 Sb 5 § per O = 2) from St. Marcel-Praborna in the Aosta Valley, Italy, were re-examined. These compositions occur in two different petrographical environments (within the rock matrix or as microinclusions within Sb-rich titanite) in the manganese concentrations at this locality. The new data confirm our earlier hypothesis that two distinct petrogenetical/crystal-chemical processes both occurred: 1. Sbmetasomatism of pre-existing Sb-free rutile inclusions; and 2. creation of neoblastic Sb-rich futile by the expulsion of Ti from pre-existing Sb-free titanite being metasomatized by Sb to form Sb-rich titanite. In the literature, Sb in minerals is variably considered as being trivalent and/or pentavalent. This work demonstrates that within rutile it is entirely Sb 5+, substituting for Ti 4 § by the following heterovalent cation exchange mechanism which is also the dominant one in the host Sb-rich titanite: 2 viR4+ = viR3+ + viR5+, where viR3+ = (A1,Cr,Mn,Fe) 3 § A near-perfect correlation of Y.R 5 § vs. ER 3 § (r > 0.98) is perturbed only by the presence of trace amounts of Ca 2+, Sr 2+ and Ba 2+. Traces of Mn 4+, Si n+ and/or (OH)-might also be present. These alkaline earth cations are the largest cations ever recorded in the rutile structure and are seemingly too large to occupy normal octahedral sites. The cation exchange mechanism involved might be that found in the 'trirutile' mineral group: 3 viR4+ = viR2+ + 2 ViR5+. Alternatively these large divalent cations may be situated in the lozenge-shaped tunnels of the rutile structure, by analogy with other large cations occupying the wider subrectangular tunnels in the analogous cryptomelane/hollandite/priderite, romandchite and todorokite mineral groups. This leads to a possible new cation exchange mechanism for the rutile structure: 2 ViR4+ + tunnelvacant = 2 viR3+ + tunnelR2+.

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Nanoparticles in natural beryllium-bearing sapphire: incorporation and exsolution of high field strength elements in corundum

Jin,

Saxey,

Quadir

et al. 2024

Contrib Mineral Petrol

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The mechanism of exsolution of hematite from iron-bearing rutile

Cited by 31 publications

References 11 publications

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Sb-rich rutile in the manganese concentrations at St. Marcel-Praborna, Aosta Valley, Italy: petrology and crystal-chemistry

Nanoparticles in natural beryllium-bearing sapphire: incorporation and exsolution of high field strength elements in corundum

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