Mineralogical Anomalies in the Darling Ranges Bauxites of Jarrahdale, Western Australia

Grubb, P. L. C.

doi:10.2113/gsecongeo.66.7.1005

Cited by 21 publications

(26 citation statements)

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“…Transmission electron micrograph of the corundum residue from HCI digestion of synthetic hematite sample # 35 that had been heated to 900~ Corundum occurs as aggregates of sub-rounded, platy crystals. similar to corundum in lateritic profiles in the Darling Range of Western Australia (Grubb, 1971 ;Anand & Gilkes, 1987c). Values of particle size derived from electron microscopy were comparable to values for diffracting domains in a direction normal to (110) ( Table 3), indicating that the particles of corundum consisted of single, coherently-diffracting domains (i.e.…”

Section: Corundummentioning

confidence: 60%

“…In soils and sediments it may occur in the clay fraction as a normal detrital mineral or may rarely be formed by hydrothermal alteration (Jackson et al, 1948). It is unlikely that corundum crystallizes under ambient weathering conditions, but it occurs in some lateritic soils formed from rocks that do not contain corundum (Grubb, 1971). It may have formed by heating of soil in bush fires (Anand & Gilkes, 1987c), and this paper is concerned with an aspect of this process.…”

mentioning

confidence: 99%

“…Studies of the distribution of microcrystalline, non-detrital corundum in soils have revealed near-surface concentrations of corundum associated with maghemite (y-Fe203) and hematite (0t-Fe203) in the duricrust and pisolitic gravel horizons of bauxites and other laterites in south-west Australia (Grubb, 1971). Anand & Gilkes (1987c) demonstrated a strong association between corundum and maghemite in these horizons and suggested a mechanism for the formation of these minerals involving a single parent mineral.…”

mentioning

confidence: 99%

“…Anand & Gilkes (1987c) demonstrated a strong association between corundum and maghemite in these horizons and suggested a mechanism for the formation of these minerals involving a single parent mineral. Grubb (1971) proposed the dehydration of aluminous goethite as a mechanism for the formation of 9 1989 The Mineralogical Society corundum in these materials. Aluminium substituted for Fe within the goethite structure may be exsolved as corundum in response to the structural transformations of goethite to hematite or maghemite that are produced by thermal dehydroxylation.…”

mentioning

confidence: 99%

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The formation of corundum and aluminous hematite by the thermal dehydroxylation of aluminous goethite

1989

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Dehydroxylation of synthetic and natural goethites with a range of AIsubstitution from 0-28 mole~o was investigated with a view to predicting the behaviour of soil goethites heated by bush fires. Hematites formed at temperatures < 500~ retain the initial A1-content of the precursor goethite up to a maximum of 28 mole% A1. Loss of A1 from the hematite structure occurred at 700~ for synthetic hematites with levels of substitution > 18 mole% A1, but no crystalline alumina phase was present. Crystallization of corundum occurred for synthetic Al-goethites with levels of substitution > 18 mole~o when heated at 900~ Formation of corundum reduces the maximum level of Al-substitution in hematites to ~ 12 mole~o. The exsolved corundum occurs as aggregated, platy crystals, 40-45 nm in diameter, containing a maximum of 7 mole% Fe. Al-substituted maghemite (7 mole% A1) formed from high AIgoethites heated at 900~ Although some corundum in soils may be produced by heating of aluminous goethite by fires, the absence of corundum in natural Al-goethites calcined at 900~ and the very high temperature (900~ at which corundum formed from synthetic goethite suggest that other sources of AI may be required as precursors for the corundum formed by heating of soils.Corundum is a common accessory mineral of silica-undersaturated, high-grade igneous and metamorphic rocks and thermally metamorphosed sediments (Deer et al., 1962), but it would not be expected to crystallize during low-temperature metamorphism. Corundum can be formed in the laboratory by the high temperature (~ 1200~ calcination of the aluminium tri-hydroxides (Rooksby, 1961), and by the topotactic transformation of diaspore (ct-AIOOH) at 450-580~ (Brown, 1980

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Section: Corundummentioning

confidence: 60%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The formation of corundum and aluminous hematite by the thermal dehydroxylation of aluminous goethite

1989

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“…The upper mottled zone and duricrust which comprise the bauxite were not sampled in this work since they may not be in situ weathering products. Grubb (1971) interpreted variations in the abundance and shape of heavy mineral grains in the upper horizons of these soils as evidence for a veneer of sedimentary material. Profiles R and L are 12 m deep and situated 1 m apart.…”

Section: Methodsmentioning

confidence: 97%

Scanning Electron Microscope Morphology of Deeply Weathered Granite

Gilkes

Suddhiprakarn

Armitage

1980

Clays and clay miner.

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Abstract--Laterite profiles developed from granite in southwestern Australia were studied by scanning electron microscopy. The morphology of soil materials reflects the mineralogy of secondary minerals formed from feldspar. In the saprolite, etched feldspar surfaces are coated with kaolinite or radiating, spherical aggregates of tubular halloysite. In the lower pallid zone these minerals have replaced most of the feldspar. In the upper pallid zone a porous framework has developed consisting mainly of quartz and gibbsite with 5-/xm euhedral gibbsite crystals in voids. Halloysite crystals in the upper pallid zone are partly unrolled and have splayed ends. Differences in mineralogy and morphology between profiles are thought to be due to variations in the intensity of leaching.

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Thermodynamics and crystal chemistry of the hematite-corundum solid solution and the FeAlO 3 phase

Majzlan

Navrotsky

Evans

2002

Physics and Chemistry of Minerals

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High-temperature oxide-melt calorimetry and Rietveld refinement of powder X-ray diffraction patterns were used to investigate the energetics and structure of the hematite-corundum solid solution and ternary phase FeAlO 3 (with FeGaO 3 structure). The mixing enthalpies in the solid solution can be described by a polynomial DH mix ¼ WX hem (1)X hem) with W ¼ 116 ± 10 kJ mol)1. The excess mixing enthalpies are too positive to reproduce the experimental phase diagram, and excess entropies in the solid solution should be considered. The hematite-corundum solvus can be approximately reproduced by a symmetric, regular-like solution model with DG excess ¼ (W H)TW S)X hem X cor , where W H ¼ 116 ± 10 kJ mol)1 and W S ¼ 32 ± 4 J mol)1 K)1. In this model, short-range order (SRO) of Fe/Al is neglected because SRO probably becomes important only at intermediate compositions close to Fe:Al ¼ 1:1 but these compositions cannot be synthesized. The volume of mixing is positive for Al-hematite but almost ideal for Fe-corundum. Moreover, the degree of deviation from Vegard's law for Al-hematite depends on the history of the samples. Introduction of Al into the hematite structure causes varying distortion of the hexagonal network of oxygen ions while the position of the metal ions remains intact. Distortion of the hexagonal network of oxygen ions attains a minimum at the composition (Fe 0.95 Al 0.05) 2 O 3. The enthalpy of formation of FeAlO 3 from oxides at 298 K is 27.9 ± 1.8 kJ mol)1. Its estimated standard entropy (including configurational entropy due to disorder of Fe/Al) is 98.9 J mol)1 K)1 , giving the standard free energy of formation at 298 K from oxides and elements as +19.1 ± 1.8 and)1144.2 ± 2.0 kJ mol)1 , respectively. The heat capacity of FeAlO 3 is approximated as C p (T in K) ¼ 175.8) 0.002472T) (1.958 • 10 6)/T 2) 917.3/T 0.5 +(7.546 • 10)6) T 2 between 298 and 1550 K, based on differential scanning calorimetric measurements. No ferrous iron was detected in FeAlO 3 by Mo¨ssbauer spectroscopy. The ternary phase is entropy stabilized and is predicted to be stable above about 1730 ± 70 K, in good agreement with the experiment. Static lattice calculations show that the LiNbO 3-, FeGaO 3-, FeTiO 3-, and disordered corundum-like FeAlO 3 structures are less stable (in the order in which they are listed) than a mechanical mixture of corundum and hematite. At high temperatures, the FeGaO 3-like structure is favored by its entropy, and its stability field appears on the phase diagram.

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Mineralogical Anomalies in the Darling Ranges Bauxites of Jarrahdale, Western Australia

Cited by 21 publications

References 0 publications

The formation of corundum and aluminous hematite by the thermal dehydroxylation of aluminous goethite

The formation of corundum and aluminous hematite by the thermal dehydroxylation of aluminous goethite

Scanning Electron Microscope Morphology of Deeply Weathered Granite

Thermodynamics and crystal chemistry of the hematite-corundum solid solution and the FeAlO 3 phase

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