Iron Meteorites
Iron meteorites are composed largely of nickel-iron metal, and most
contain only minor accessory minerals. These accessory minerals often
occur in rounded nodules that consist of the iron-sulfide troilite or
graphite, often surrounded by the iron-phosphide schreibersite and the
iron-carbide cohenite. Despite the fact that some iron meteorites contain
silicate inclusions, most have fundamentally the same superficial
appearance.
Presently, iron meteorites are classified under two established systems.
Just a few decades ago, iron meteorites were exclusively classified
according to the macroscopic structures revealed when their polished
surface was etched with nitric acid. Depending on these structures, they
were separated into three classes: octahedrites, hexahedrites, and
ataxites.
IIG Group
This is a brand-new group of iron meteorites, recently under
publication. Formerly known as the Bellsbank grouplet, it consists of just
five members: Bellsbank, La Primitiva, Tombigbee River, Twannberg, and the
recently discovered Guanaco, a meteorite that was found in the Atacama
Desert, Chile, in 2000. Structurally, the irons of the IIG group are
hexahedrites or coarsest octahedrites. In their structural and elemental
compositions they resemble the iron meteorites of group IIAB, but they
contain even less nickel and unusual, abundant ribbons of the
iron-phosphide schreibersite. These ribbons often cover 15% of the etched
surface of a IIG iron. This suggests that the formation of the IIG irons
occurred in the outer regions of the core of a differentiated asteroid,
probably distinct from the IIAB parent body
Twannberg
SWITZERLAND,
IRON METEORITE
Place
of find: Nidau district, canton Bern, Switzerland.
47°7'28"N.,7°10'44"E.
Date
of find: 9 May, 1984
Classification:
Iron (IIG)
Total
weight: 15.91 kg
Circumstances
of find: Found in a barley field, after ploughing.
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Twannberg 00
103.65 gr
A rare Switzerland historical meteorite, nearly imposible to
get !
Price on request
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