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Meteorite
Name: GIBEON
Class: Iron Meteorite IVA
fine
Octahedrite 0.3 mm
contains rare silica inclusions
Country: NAMIBIA
Date: Find: 1836
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The Gibeon
meteorite shower is the most extensive meteorite shower known
on Earth which covers a large elliptical area of some 275 by
100 kilometers centered on Brukkaros south of Mariental. Most
fragments fell just southeast of Gibeon. To date, some 120 specimens
with a weight of almost 25 tons have been recorded. In addition
an unknown number have been collected but never recorded.
Small pieces of metal were collected by James Alexander in 1838
at a place about three days journey northeast of the mission
at Bethany. He described the pieces as being up to two feet
square, and sent some materials to the chemist John Herschel
in London, who established their meteoritic origin. However,
it is well known that the local Nama people had been using the
meteorites for a long time to produce spear points and other
weapons.
The first large piece of some 81 kg was carried by ox-wagon
for 800 miles to Cape Town by John Gibbs before 1853. From there
it was sent to London, where the mineralogist to Queen Victoria,
Professor John Tennant, purchased it. He forwarded it via New
York to Professor Charles Shepard of Amherst College in Massachusetts,
who studied the material in detail. By 1910, at least ten pieces
of the Gibeon Meteorites had been shipped to Europe. From 1911
to 1913, the geologist of the German colonial administration,
Dr Paul Range, collected all the remaining meteorites he could
find and mapped their occurrence. The specimens were displayed
in Windhoek, and a number of them were also donated to various
museums around the world.
The Gibeon Meteorites occur partially embedded in rocks of the
Karoo Sequence and calcretes of the Kalahari group. It has been
calculated that a meteorite body, measuring roughly 4 by 4 by
1.5 meters must have entered the Earth's atmosphere along a
northwesterly trajectory and at a low angle of 10` to 20` from
the horizon. This body fragmented while still high in the atmosphere,
so that the fragments themselves suffered thermal alteration
by melting of the outer surface.
This either covered the fragments in smooth outer layers, or
was pulled off in places by the drag of the atmosphere, leaving
an uneven mass with deep, spherical cavities on the outer surface.
These well-developed thermal alteration structures prove that
the fragments had an extended flight through the atmosphere
before being deposited. The varieties of thermal and shock-induced
microstructures of the Gibeon Meteorites are the greatest in
the world and only matched by the Canyon Diablo Meteorite of
northern Arizona.
The Gibeon
Meteorites are classified as octahedrites, the most common type
of iron meteorite, and consist entirely of taenite and kamacite,
two different crystalline varieties of a iron-nickel-alloy.
Taenite (gamma-Fe with 8-55% Ni) and kamacite (alpha-Fe with
5.5% Ni) form alternating parallel crystal bands that are arranged
in a triangular pattern. This pattern is the typical Widmannstätten
structure, a characteristic feature of many meteorites. Besides
iron, the main constituent, the Gibeon Meteorites contain an
average of 8% nickel, 0.5% cobalt, 0.04% phosphorus, small amounts
of carbon, sulphur, chromium and copper, and traces of zinc,
gallium, germanium and iridium. The Gibeon Meteorite specimens
range in size from one ton to just a view grams. A few rare
tetrahedral and octahedral crystals have also been recovered,
and probably resulted from the successive splitting off of thin
kamacite lamellae along with the selective corrosion of intervening
taenite layers.
Today, the
known Gibeon Meteorites that have remained in Namibia are displayed
in the Post Street Mall and at the museum of the Geological
Survey of Namibia in Windhoek. A number of smaller ones also
form part of the reference collection of the Geological Survey
of Namibia. While meteorites continue to be found in the area
of Gibeon, it is very difficult to observe them in the field
without a metal detector. Despite the fact that meteorites are
protected by law in Namibia, and may not be removed from their
original site, a large number are leaving the country illegally
to be sold at international rock and mineral shows. The largest
specimen known and weighing about one ton was illegally exported
to the USA recently. This, sadly, deprives the local people
of an opportunity to develop a sustainable use out of this unique
natural resource and national heritage; it also deprives the
international scientific community of valuable research material.
(Ref. Allgemeine Zeitung Namibia 18.04.2001)
Here
you surely not only have an esthetically most beautiful piece
of meteorite, but also one with history. The meteorite is a
piece from 'out of this world', approx. 4.5 billion years old
with its origin in the asteroid belt between Mars and Jupiter.
It
is a beautiful individual, showing nice Widmanstätten Pattern
when etched, your
own little piece of heaven! We
hope you have lots of enjoyment with it!
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