[meteorite-list] Tschermak and Bustites

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:11 2004
Message-ID: <DIIE.0000004000001DF5_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

II. The magnesium-rich stones, poor in metallic iron: Bustites

This type, a mixture of diopside and enstatite, is represented thus far only by
the meteorite Bustee (near Goruckpur; fell December 2, 1852). Maskelyne (1870a)
has studied it and has measured and analyzed its constituent minerals. Its fabric
consists of crystals and large fragments. Flight (1875) has published a picture of
the stone, which clearly shows this heterogeneous mixture. The stone has no crust.

Diopside, the principal mineral, appears gray to violet by incident light. Maskelyne was
able to determine the prism zone and a pyramid face on the grains. Conspicuous in this
constituent is a fine lamellar structure parallel to ... , which is often related to a
polysynthetic twinning on this surface. Besides this foliation, which is similar to the
structure of diallage, lamellae and distinct twinning parallel to ... are also frequently
present.

The numerous inclusions are black; some are needle-shaped and oriented parallel to the
.. foliation, others are rounded. They account for the mineral's violet pigmentation.
The enstatite is often euhedral. Maskelyne was able to determine only the prism zone. He
distinguished three types of enstatite: gray and opaque, gray-white and transparent, clear
and colorless. Different types can also be recognized in thin-section. Gray enstatite contains
numerous glass inclusions, some of which contain (immobile) bubbles. The inclusions often
have polygonal outlines and appear to be negative crystals filled with a pale brownish glass.
When it contains many such inlusions the enstatite is cloudy, but some colorless fragments
are quite free of inclusions.

Besides diopside and enstatite, Bustee contains subordinate amounts of plagioclase,
oldhamite, nickel-iron, and osbornite. Plagioclase was not identified by Maskelyne;
it appears to be present only in very small amounts, as colorless fragments almost
free of inclusions and without twin lamellae. This mineral resembles in all respects
the plagioclase in Bishopville. Oldhamite, CaS, is present in only one part of the stone,
in rounded grains with cubic cleavage. Nickel-iron is scarce. Osbornite, which is very
scarce, occurs in octahedra and gives the reactions for sulfur, calcium, and titanium
or zirconium.Maskelyne thinks the inclusions in the diopside may be osbornite.
Received on Tue 06 Apr 2004 04:34:51 PM PDT