A calcium-aluminum-rich inclusion from the Essebi (CM2) chondrite: Evidence for captured spinel-hibonite spherules and for an ultra-refractory rimming sequence

Goresy, A. El; Palme, H.; Yabuki, Hideo; Nagel, K.; Herrwerth, I.; Ramdohr, P.

doi:10.1016/0016-7037(84)90224-2

Cited by 44 publications

(18 citation statements)

References 25 publications

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“…The principal secondary minerals in CM CAIs are diverse phyllosilicates (cronstedtite, serpentine, and the FeNi-S-O-phase tochilinite; see review by Tomeoka et al, 1989) and calcite. Feldspathoids have only rarely been reported (El Goresy et al, 1984;MacPherson et al, 1983). …”

Section: Chondritesmentioning

confidence: 97%

Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites

MacPherson

2014

Treatise on Geochemistry

105

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Section: Chondritesmentioning

confidence: 97%

Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites

MacPherson

2014

Treatise on Geochemistry

105

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“…If meteoritic UNK formed by such a mechanism, then extreme rare earth element (REE) enrichments would be expected whereas its REE content would be expected to be low if it hadexsolved from the surrounding melilite. The UNK described by El Goresy et al (1984) is REE enriched and, therefore, consistent with crystallization from a melt, but the host inclusion is so unusual that it is not possible based on this occurrence to make general inferences about occurrences of UNK. in the Allende CAIs described here.…”

Section: Origin Of Unkmentioning

confidence: 99%

A new titanium‐bearing calcium aluminosilicate phase: I. Meteoritic occurrences and formation in synthetic systems

et al. 1994

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A new titanium‐bearing calcium aluminosilicate mineral has been identified in coarse‐grained calcium‐aluminum‐rich inclusions (CAIs) from carbonaceous chondrites. The formula for this phase, which we have temporarily termed “UNK,” is Ca3Ti(Al, Ti)2(Si, Al)3O14, and it is present in at least 8 of the 20 coarse‐grained CAIs from the Allende CV3 chondrite examined as part of this project. The phase occurs in Types A and B1 inclusions as small tabular crystals oriented along two mutually perpendicular planes in melilite. UNK crystallizes from melts in dynamic crystallization experiments conducted in air from four bulk compositions modeled after Types A, B1, B2 and C inclusions. Cooling rates resulting in crystallization of UNK ranged from 0.5 to 200 °C/h from maximum (initial) temperatures of 1375 to 1580 °C. Only below 1190 °C does UNK itself begin to crystallize. To first order, the presence or absence of UNK from individual experiments can be understood in terms of the compositions of residual melts and nucleation probabilities. Compositions of synthetic and meteoritic UNK are very similar in terms of major oxides, differing only in the small amounts of trivalent Ti (7–13% of total Ti) in meteoritic samples. UNK crystallized from the Type A analog is similar texturally to that found in CAIs, although glass, which is typically associated with synthetic UNK, is not observed in meteoritic occurrences. A low Ti end‐member of UNK (“Si‐UNK”) with a composition near that of Ca3Al2Si4O14 was produced in a few samples from the Type B1 analog. This phase has not been found in the meteoritic inclusions.

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“…Basal orientations of the crystals exhibited six flattened hexagonal bipyramids; some apparently prismatic forms were also observed. The papers by El Goresy et al (1984) and Paque et al (1986) reporting the occurrence of a Ti-bearing Al-silicate, which we refer to as UNK for the purposes of this paper, in meteoritic inclusions and slag-like synthetic compositions, raised the possibility that the furnace slag crystals were also the UNK phase. This idea has been confinued, as described below, and has led to use of crystals from the slag for the determination of the space group of the mineral described in Paque et al (1986Paque et al ( , 1994 and Barber et al (1994) by means of convergent beam electron diffraction (CBED).…”

mentioning

confidence: 91%

A new titanium‐bearing calcium aluminosilicate phase: III. Crystals from a mixer furnace slag

Barber

Agrell

1994

Meteoritics

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Small crystals of an optically uniaxial Ti‐bearing calcium aluminosilicate were discovered in a mixer furnace slag consisting mostly of åkermanitic melilite. The crystals have the same unit cell as those observed for a phase crystallized from slowly‐cooled melts used to simulate the formation of aluminous inclusions in meteorites. Moreover, compositions of synthetic and meteoritic occurrences of the phase are all very similar and can be expressed in terms of a binary solid solution between the end‐members Ca3TiAl2Si3O14 and Ca3Ti(AlTi)(AlSi2)O14. Thus, crystallographic and crystallochemical information obtained from crystals in the mixer furnace slag can be used to constrain the origin of similar crystals found in meteoritic inclusions. We separated crystals from the mixer furnace slag by acid leaching; some were used for EPMA analysis, others were crushed for study by TEM methods or X‐ray powder diffraction. Convergent beam electron diffraction shows that the crystals belong to the trigonal (rhombohedral) class and have point group symmetry 3m. X‐ray powder diffraction gives the unit cell parameters a = 0.791 ± 0.009 nm, c = 0.492 ± 0.006 nm. The results suggest that the mineral has space group symmetry P3ml or P31m.

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A calcium-aluminum-rich inclusion from the Essebi (CM2) chondrite: Evidence for captured spinel-hibonite spherules and for an ultra-refractory rimming sequence

Cited by 44 publications

References 25 publications

Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites

Calcium–Aluminum-Rich Inclusions in Chondritic Meteorites

A new titanium‐bearing calcium aluminosilicate phase: I. Meteoritic occurrences and formation in synthetic systems

A new titanium‐bearing calcium aluminosilicate phase: III. Crystals from a mixer furnace slag

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