[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Intertesting Gao (Upper Volta) Specimen



Gene wrote:
I'm more interested, however, in discussing the formative processes of large
metal inclusions in chondritic meteorites and its implication of a
nonhomogeneous or nonlinear solar nebula ...

The Slovak, Arkansas, H5 chondrite also shows such large metal nodules. Cp. D.W.G. Sears' booklet Thunderstones:

1) B-W photo, p. 21,: Figure 8. Photograph of two cut and polished faces of the Slovak meteorite showing the LARGE METAL NODULES present in this meteorite. It is widely assumed that an impact in space caused the small metal grains to coalesce into large nodules.

2) Text passage, pp. 61-62: As a rule, the H chondrites are less heavily shocked than the L chondrites, but many of them are black, and the Slovak meteorite contains large nodules of metal which are commonly regarded as the result of shock.

3) My 40.5 gram Slovak specimen (dimensions: 6.0 x 3.7 x 0.5 cm) shows one elongate inclusion approximately 14 mm by 5 mm with troilite intergrowths. This inclusion doesn't show through to the other side, either. One of the cut and polished 0.5 cm surfaces shows another nodule (0.6 x 0.3 cm) 'in profile'. It doesn't extend to the other side, either. Instead, this nodule stops short of reaching the other side. There is a third almost circular (0.7 x 0.5) nodule close to one crusted edge, and here again, no sign of showing through. There's a fourth, small patch on the rear side which might belong to the large elongated inclusion mentioned above. By the way, the large elongated inclusion is the only one that harbors troilite 'bands'. The other inclusions are free from troilite.

Some interesting references:

V.P. SEMENENKO et al., The two types of metal particles in the Bachmut meteorite (Abstracts from Meteoritika in Meteoritics 23-4, 1988, p. 383).

C.E. HOLLAND-DUFFIELD et al. (1991) The structure and composition of metal particles in two type 6
ordinary chondrites (Meteoritics 26-2, 1991, pp. 97-103).

C.W.YANG et al. (1994)New Cooling-Rate Indicator For Metal Particles in Meteorites (Meteoritics 29-4, 1994, p. A553).

G. PEDRAZZI et al. (1996) Tetrataenite in metal particles of the Trenzano meteorite identified by Mössbauer spectroscopy (Meteoritics 31, 1996, A105).

T.J. McCoy et al. (1997) The Leedey, Oklahoma, chondrite: Fall, petrology, chemistry and an unusual Fe,Ni-FeS inclusion
(Meteoritics 32-1, 1997, pp. 19-24):
Abstract - The Leedey, Oklahoma meteorite shower fell on Nov. 25, 1943, following a fireball which was visible across much of southwestern Oklahoma and northcentral Texas. The shower produced 24 stones with a total mass of ~51.5 kg. The stones formed a strewnfield ~18 km in length in the same direction as the observed path of the meteor (N50 °W). Leedey is classified as an L6(S3) ordinary chondrite. We report bulk major element chemical analyses from four separate laboratories. Leedey contains an unusual 6 by 8 mm composite Fe,Ni-FeS grain, which is composed of a 3 mm kamacite grain adjacent to a 5 mm troilite grain. A 50-100 µm rim of high-Ni (45-55 wt.%) taenite (tetrataenite) occurs at the boundary between kamacite and troilite. A single, zoned pyrophanite grain is observed at the boundary between the inclusion troilite and host silicates. An origin as a foreign particle incorporated after metamorphism or during impact melting appears unlikely. This particle likely formed by a complex set of processes, including melting in the nebula, parent body metamorphism and reheating  by later shock, mirroring the history of the host chondrite.
 

Regards, Bernd Pauli


Follow-Ups: