[meteorite-list] Deformed Gibeon patterns

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:30 2004
Message-ID: <3C966804.905E415_at_lehrer1.rz.uni-karlsruhe.de>

Ron wrote:

> It was not uncommon to see a discontinuity where apparently crystallization
> proceeded from different regions with the Widmanstätten patterns oriented
> differently, and approached an interface between them. It's not so much a
> wedge, but rather a zone between the two areas where there is no pattern,
> and this zone can be several cm. wide.

BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Vol. 2, pp. 584-593:

Each austenite grain has, in the usual way, formed a fine Widmanstätten
pattern, but it is interesting to note that near the boundary the
pattern becomes very indistinct, apparently because only one of the four
possible Widmanstätten planes has been able to develop.

COHEN E. (1905) Meteoritenkunde, Heft III, pp. 324-342:
COHEN E. (1905) Meteorites, Volume III, pp. 324-342:

Ueber ein Meteoreisen von Mukerop, Bezirk Gibeon, Grossnamaland
On a meteoric iron from Mukerop, Gibeon region, Grossnamaland

Von A. Brezina und E. Cohen (By A. Brezina and E. Cohen).

Mit Tafel VI. (With Table VI).

The etched surface is composed of three parts which are clearly
discernible. One part comprising about 1/3 of the etched surface assumes
a matte color and a weak, greasy sheen when etched; at a cursory glance,
this sheen looks homogenous and resembles the dense, nickel-rich
ataxites. But when studied carefully, especially with a light source
infalling at a shallow angle and using a loupe, you recognize a
structure of fine octahedritic lamellae*. The reason why this structure
is so indistinctly visible is, on the one hand, due to the extremely
fine taenite lamellae, and, on the other, it is due to the bands and
fields consisting of the same fine-grained kamacite that is weakly
shimmering under the microscope.

* Footnote by the authors: Interestingly, the more you etch the less
discernible the Widmanstätten pattern becomes.
Received on Mon 18 Mar 2002 05:19:48 PM PST