[meteorite-list] TSCHERMAK G. (1885) - Part 6

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:50 2004
Message-ID: <DIIE.0000001C00001BF6_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

General Characteristics of Meteorites

Minerals and other constituents - part 2:

Anorthite

Crystals and grains of anorthite are a principal constituent of several
stones. Many stones contain grains of plagioclase which may very well
not have the composition of anorthite.

Maskelynite

This has the composition of plagioclase but is optically isotropic.

Glass

Glass is often present in meteorites, in addition to the crystalline constituents.
Some glasses are colorless, like maskelynite; others are colored, usually brown,
and often show incipient devitrification, usually into magnesium silicates.

Carbon and hydrocarbons soluble in alcohol

These have been found in black meteorites, along with a carbonate having
the properties of breunnerite. Many writers hold that the water in these stones
is secondary in origin, since most meteorites contain no water; and that sulfates
are of secondary origin, formed by the weathering of iron sulfide.

Finally, some reports speak of meteoritic constituents which have not been confirmed,
such as lead, pyrite, leucite, or sulfur, or which were given new names but later shown
to be familiar minerals, such as shepardite and piddingtonite.

Classification

G. Rose (1864) has proposed a classification of the meteorites according to their
principal minerals, which begins with the irons and ends with those stones most
similar to terrestrial rock types. This sequence is approximately in order of decreasing
specific gravity and forms a geologic column to the extent that the parallel drawn by
Daubree (1870) is correct; namely, the metallic core of the earth is the oldest structure,
and the less dense silicate masses are younger. If the meteorites are fragments of one
or several small planets, we would expect these planets to have a structure similar to
that of the earth: a metal sphere surrounded by an igneous, tuffaceous, silicate shell
(Tschermak, 1875).

Thus the Rose classification is consistent with the current conception of planetary
formation, and, for that reason, could be called the natural classification.
Received on Sun 14 Mar 2004 03:12:30 PM PST