[meteorite-list] Tschermak and Howardites - Part 1 of 2

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:11 2004
Message-ID: <DIIE.0000003700001DDB_at_paulinet.de>

TSCHERMAK G. (1885) Die mikroskopische Beschaffenheit der Meteoriten
(Stuttgart E. Schweizerbart'sche Verlagshandlung, E. Koch, 23 pp.).

English Translation: The Microscopic Properties of Meteorites, Vol. 4,
No. 6 (Smithsonian Contributions to Astrophysics, Washington, D.C., 1964).

Translation by J.A. Wood and E.M. Wood

Howardites (1)

Research to date places the meteorites Maessing, Luotolax, Bialystok, Le Teilleul,
Nobleborough, and Frankfort in this class. Of these, the first two have been most
thoroughly studied.

Luotolax has a tuffaceous texture. Greenish-yellow, white, and black fragments
and grains, as well as small fragments of eucrite, are embedded in a loose,
earthy groundmass.

The meteorite as a whole has the character of a volcanic tuff, in which various
minerals which do not normally occur together in the same rock appear side by
side in irregular fragments that seldom display crystal outlines.

Among the transparent minerals, I was able to distinguish three anorthites, four
augites, and bronzite. Anorthite in the small eucrite fragments has the same
character as that in Stannern. In both occurrences the anorthite contains minute
glass inclusions of the same form and distribution. The plagioclase which occurs
in non-eucrite fragments may be exactly like eucritic anorthite, or may contain
large dark inclusions of glass or groundmass, or may be almost devoid of inclusions.

The augite in the eucritic fragments is also identical with that in Stannern. It sometimes
occurs as brown grains having black striations and cracks filled with black material, but
usually as yellow granular augite with a finely lamellar structure. The abundant augite
fragments and grains mingled with the stone's groundmass include the two types already
described and also a third variety, greener and with a fine lamellar structure. Many of
these grains are twinned; others contain numerous needle-shaped black inclusions in parallel
array. A fourth form of augite appears as large, very pale brown fragments without lamellar
structure.

Bronzite occurs in large, very pale greenish fragments almost devoid of inclusions. This
constituent is easily recognized by its parallel extinction and its system of parallel
cleavage cracks. These yellow-green grains had previously been taken for olivine; I noted
they have the cleavage of bronzite. As further proof of this identification, the mineral
(powdered) was found not to react with concentrated hydrochloric acid.

A few small fragments in the groundmass, as well as some fine-textured polycrystalline
fragments rich in black grains, seem to me to be olivine. The dark grains and fragments
visible with the naked eye consist partly of this polycrystalline component and partly
of fine-grained to cryptocrystalline eucrite such as occurs in Stannern.
Received on Sun 04 Apr 2004 03:40:59 PM PDT