[meteorite-list] Zacatecas (1969)

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 25 Feb 2007 15:25:40 UT
Message-ID: <DIIE.000000BC00001771_at_paulinet.de>

BUCHWALD, V.F. (1975) Handbook of Iron Meteorites, Volume 3, pp.1367-1369, excerpts:

Zacatecas (1969), Zacatecas, Mexico
Approximately 22? 48'N, 102? 33W
Medium octahedrite, Om
Bandwidth 0.70?0.10 mm
Recrystallized
Group IIIAB
9.0% Ni, about 0.5% P, 20.3 ppm Ga, 38.8 ppm Ge, 0.029 ppm Ir.

History

A mass of 6.66 kg was purchased by Richard E. Dalsin of Minneapolis, Minnesota, from a
Mexican in the city of Zacatecas in February 1969. Mr. Dalsin reported that "the Mexican
told him he had found it in the area," but more could not be learned. The complete specimen
was donated to the Smithsonian Institution in December 1969.

Description

The mass has the shape of a low triangular pyramid with a height of 7 cm and a base of
15 x 16 cm. The base is a fracture surface that is rather flat, partially following one set
of Widmanst?tten planes and partially some of the large schreibersite inclusions. The mass
is evidently a corner piece of a much larger main mass which has either not been found yet
or has not been reported. As will be seen from the structural discussion below, the mass
cannot be a fragment of any of the recorded Mexican meteorites.
The surface is weathered and covered with 0.1-1 mm terrestrial oxides. Regmaglypts, 3-5 cm
across and up to 1 cm deep, are present however; even a little, weathered fusion crust may be
identified in the bottom of some of the regmaglypts. The size of the regmaglypts, suggests
that the unknown main mass is 30-50 cm in diameter. The fragment is severely hammered over an
area of several square centimeters, but there are no indications of an artificial reheating. There
are distinct marks indicating work with hammer and chisel, so it cannot be ignored that the frag-
ment might have been broken from the main mass by the finders. It appears that the finders have
widened a deep, preexisting crack and after some efforts finally detached the 6.7 kg fragment.

The fracture surface that presently terminates the specimen may have been initiated in the remote
preatmospheric shock event but was probably first fully opened after the main mass arrived on the
Earth. Many similar cases of irons with deep, but incomplete, fissures are known, e.g., Navajo,
Bacubirito, Lazarev and some Sikhote-Alin specimens.

It shall be interesting to see the main mass of Zacatecas (1969).

Although it bears some resemblance to Apoala, Chupaderos and other Mexican irons,
Zacatecas (1969) is unique in its secondary structure and may, with confidence, be said
to be different from these falls.

Specimen in the U.S. National Museum in Washington:

6.66 kg endpiece of unknown main mass (no. 5291, 16 x 15 x 7 cm)
Received on Sun 25 Feb 2007 10:25:40 AM PST