[meteorite-list] Tschermak and Chladnites

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:13 2004
Message-ID: <DIIE.0000003A00001E42_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

Chladnites

This combination of minerals has been found in only one meteorite, Bishopville.
The stone is coarse-grained and consists mostly of friable snow-white enstatite.
Rose observed other white grains, but could not identify them. I find these to be
plagioclase. The third constituent is pyrrhotite. The stone's crust has a marbled
appearance, being partly colorless, partly black, white, bluish, and gray.

Enstatite occurs in large and small grains, mostly large. I observed distinct crystal
boundaries on one of the small grains ...The grains are cut by many fine, irregular
cracks (in addition to the cracks that were produced during preparation of the thin-
section). Inclusions are rare and consist of opaque grains, less often of black needles.

Plagioclase is usually attached to the small enstatite grains. I have not found plaogioclase
with a regular crystal boundary. Its outlines are rounded, lobate, or elongated. In polarized
light a very distinct twin structure is sometimes seen, consisting either of alternating wide
and narrow lamellae, or entirely of extremely narrow lamellae having a finely-ruled appear-
ance between crossed Nicols. Most untwinned plagioclase grains show undulose extinction;
many are aggregates of several small grains. The identification of this mineral as plagioclase
is based on its behavior in polarized light. An attempt to separate individual grains from the
stone for further tests was unsuccessful, not only because of their small size but also because
they could not be distinguished by color or luster from the enstatite.

In places, the plagioclase shows streaks and slight cloudiness and is brownish by transmitted
light. Small opaque inclusions are rare, but larger, often spindle-shaped, bronzite inclusions
are abundant. Pyrrhotite forms large and small grains; in the specimen studied these grains are
surrounded by brown areas, the result of reaction with the atmosphere.

The analysis of Rammelsberg (1861), which found Al2O3, CaO, and alkalis in small amounts, in
addition to the ingredients of enstatite, is in full agreement with the microscopic description
just given.

Rose also reports small amounts of nickel--iron and a black mineral that sometimes fills fine
cracks. Breaking the stone along such cracks, I observed a shiny material, similar to that in
meteorites to be described later, in which the veins consist of iron, pyrrhotite, and silicate
glass.
Received on Sat 10 Apr 2004 03:46:15 PM PDT