[meteorite-list] Tschermak and Eucrites - Part 2 of 3

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:55 2004
Message-ID: <DIIE.0000003B00001D3E_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


Description of Meteorite Types

The calcium-rich stones, poor in metallic iron - Eucrites:

Juvinas, Stannern, Jonzac

The extinction angle is 52=B0 10', compared with an extinction angle of 51=B0 06' for
diopside from Ala (Italy). In sections parallel to ... and ..., numerous thin lamellae
parallel to ... can be seen. This is almost certainly a polysynthetic twinning ..., as
is the case in diopside of lamellar structure. The black color of the augite is caused
by countless inclusions, mostly black but occasionally brown, which are both needle-
shaped and rounded in form. The brown, rounded inclusions have the appearance of glass;
the nature of the needle-shaped ones cannot be determined. The rounded and dust-like
inclusions tend to form layers parallel to ... Augite in the massive portion of the
stone occurs as incomplete crystals or anhedral grains, full of the inclusions discussed
above and often divided by cracks. Along the walls of the cracks, inclusions are often
so sparse that the pale brownish color of pure diopside can be seen. On the other hand,
these cracks are filled with a black material, as if the substance of the inclusions had
migrated from the walls into the cracks. Another constituent is the yellow silicate mineral
which, in the form of small plates, Rose has observed. These occur here and there in the
groundmass, often projecting into or across the druses. In thin-section the plates are seen
to consist of tiny grains of pale brownish color and to have the same fine lamellar texture as
the augite described above. Since this mineral also fuses to yield a black glass, it almost
certainly is diopside without black inclusions. Thus, these little plates seem to be pseudo-
morphs after some unknown silicate. In thin-section this yellow silicate is seen to occur not
only in the form already described, but also as irregularly distributed granular particles in
the groundmass, and filling the interstices between small anorthite crystals in the groundmass.
Received on Sun 28 Mar 2004 04:56:16 AM PST