Gibeon Meteorites Namibia
This was the largest known of shower of extra terrestrial bodies ever to fall to
GIBEON METEORITES NAMIBIA. This was the largest known of shower of extra terrestrial bodies ever to fall to earth. On display in the Post Street Mall Windhoek.
Gibeon Meteorites Post St. Mall Windhoek
If you have an interest in meteorites, Namibia has a couple of attractions that you won't want to miss. In the north, not far from Grootfontein is the Hoba Meteorite which is the largest knownof metal meteorite in the world, and beautifully displayed right in the middle of Windhoek are a selection of the Gibeon Meteorites, which are the largest known shower of extra terrestrial bodies ever to land on Earth. The exact number of the Meteorites discovered is unknown as many have been smuggled out of the country over the years. To date a total of 120 pieces have been recorded as having an almost identical composition and are thought to have initially formed a body weighing in excess of 15 ton.
Gibeon Meteorite Display
Situated in the Post Street Mall consists of 33 pieces weighing between 195kg and 555kg and numbers the larger specimens that presently remain in Namibia. It offers you a unique opportunity to view some of the oldest and rarest known of material to man. Radiometric dating has aged them at 4 billion years old.
It is thought that the original body that comprised the Gibeon Meteorites would have been about 4 x 4 x 1.5 m and would have fragmented shortly after entering the earth's atmosphere at a low trajectory from a north-westerly direction and that the pieces experienced burn-out causing their surface structure to alter. On the final stage of their journey while burning through the earth's atmosphere the meteorites were thermally altered. The indentations on the surface can clearly be seen.
One of the Gibeon Meteorites has been sliced in two parts in order that the interior of the body can be seen. The metal is resistant to corrosion owing to the percentage of Nickel.
- Astronomical Origin: Thought to have been from an exploding supernova over 4 billion years ago.
- Classification - Octahedrite: The most common form of Iron-Alloy meteorites. The composition is:
- 87% iron, 8% nickel ( Taenite, Gamm-fe with 8,5%: Kamacite, Alpha-fe with 5,5% nickel - see Widmanstatten Pattern below), 0,5% cobalt, 0,04% phosphorus with small amounts of carbon, sulphur, chromium. Traces of zinc, gallium, germanium and iridium are present.
- Meteor Trajectory: Approximately 20 degrees from North -Westerly direction
- Collision with Earth: Unknown, estimated between 200 - 220 million years ago
- Location Of Landing: Elliptical area 275 x 100 km (171 x 62 miles) Gibeon Area.
- Weights of Meteorites: range from a few grams to in excess of 1 ton.
Gibeon Meteorites - The 'Discovery': The first European to make record of the unusual ' metal rocks' that became known as the Gibeon Meteorites was the British explorer Sir James Edward Alexander in 1838 when travelling north of the Bethany mission station. His enquiries of the local Nama people established that they valued the metal pieces and when found, had been smelting them for use as spear and arrow-heads for some generations.
He sent samples of the metallic objects to London for the attention of the respected chemist John Herschel, where it was established that they were of meteoritic origin.
N amed after Count Alois Von Beckh Widmanstatten (1753 to 1849) an Austrian printer and scientist who noted that when the machined surface of an iron - nickel meteorite was etched with acid a distinct cross-hatched pattern appeared on the flat metal face. This crystalline structure is unique to metal
bodies, such as meteorites, that have formed in space, and happens when a molten metal meteorite having a composition of about a 90% percent iron and 10% nickel begins to cool. Calculations indicate that this cooling process, which takes place under zero gravity conditions, is extremely slow, being approximately 2°c per million years. As the temperature of the metal alloy meteorite slowly lowers to about 700°c the meteorite would still be in a liquid form, but within this approximate temperature range, bands of crystals of the two associated metals kamacite and taenite would begin to be formed in a process know as diffusion. (kamacite being formed in the low nickel phase while taenite is formed during the high nickel phase). At this temperature the composition of the kamacite would be about 4% nickel. Over a period of some further 200 million years the meteor's temperature would have cooled to about 600°c during which period the migration of nickel atoms within the cooling molten metal mass would have increased the nickel composition of the bands of kamacite to about 6% , Whereas the bands of taenite would have risen to have a nickel content of approximately 19%. At approximately 500°c the migration of the atoms ceases. The resultant crystalline structure of the metal mass is of a cross-hatched formation now named as the Widmanstatten Pattern. This condition is not found on any metal bodies originating on planet earth.
Acknowledgements and further reading: G1, G2, H12, P1
Of Interest: T here is a further collection of 9 of the Gibeon Meteorites on display in the Museum of the Ministry of Mines and Energy - Department Of Geological Survey Museum . plus 1 in the museum at Rehoboth
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