Gibeon Meteorites

Gibeon Meteorites

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 known-of metal meteorite in the world, and displayed right in the middle of Windhoek is the largest known shower of extra terrestrial bodies ever to land on Earth is known as the Gibeon Meteorites. The exact number of the Gibeon 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.

 

The display 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.

 

Gibeon Meteorites

A National Heritage Site

Gibeon Meteorites Post St. Mall Windhoek

Like stainless steel

Burn pattern

 

It is thought that the original body 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 Gibeon  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 Gibeon Meteorites 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 100km (171 x 62 miles) Gibeon Area.
• Weights of Meteorites: range from a few grams to in excess of 1 ton.

 

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. 

 

In 1853 John Gibbs transported by ox-wagon an 81kg sample sample of the Gibeon Meteorites to Cape Town, from where it was shipped to London. The meteorite was purchased by Prof. John Tennant a mineralogist and to America.

 

Between 1911-1913 the Chief Geologist for the Colonial Administration of German South West Africa prospected the area and collected the know of remaining Gibeon Meteorites specimens which were brought to Windhoek, from where a number were donated to foreign museums and prominent collectors.

 

Meteorites are now protected by strict laws in Namibia. It is an offence to even move one from its resting place.

 

Widmänstatten Pattern:

Named after Count Alois Von Beckh Widmänstatten (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 Widmänstatten Pattern. This condition is not found on any metal bodies originating on planet earth.

 

Acknowledgements and further reading: G1, G2, H12, P1 

Local Area Attractions and Articles of Associated Interest.

► Alte Feste Museum    ►Daan Viljoen Game Reserve    ►   Heroes' Acre   ►  Windhoek

► Geological Time-Table     ►  Hoba Meteorite   

 

Did You Know ?

• There 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

• Map of Namibia   For detailed digitally produced road and town directional maps of Namibia

• Namibia-Tour-Guide   A site designed specifically, to help you plan your tour of Namibia

• Namibia-Accommodation-Guide The complete list as registered with the Namibia Tourism Board

• Namibia-Hunting-Safaris All you need to know, plus the complete list of licensed, registered Professional Hunters

• Air-Namibia-Timetable User friendly timetable of all Air Namibia flights.

• South-African-Airways-Timetable  User friendly timetable of all SAA flights.

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Gibeon Meteorites

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