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Gibeon   contributed by Steve Brittenham, IMCA 2184   MetBul Link
 
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View all entries for   Meteorite (45)   Steve Brittenham (108)


Copyright (c) Steve Brittenham.
50 kg individual, 4.6 kg 100 mm diameter sphere, and a 180 mm Damascus letter opener fashioned from Gibeon metal.   Iron, IVA

TKW 26 metric tons. Fall not observed. Found 1836 in Great Namaqualand, Namibia. The fragments of the meteorite in the strewn field are dispersed over an elliptical area 275 km long and 100 km wide.

and .



   


Steve writes:
The Gibeon meteorite is very well known, and some argue it has one of the most beautiful Widmanstӓtten patterns of all the irons. MPOD already has several wonderful examples of it, but like Sikhote-Alin, there can never be enough, so I humbly submit a few more here. And Paul, per your 8/20/2105 question, the 50 kg specimen rings with a constant frequency pretty much wherever it’s hit, while the 4.6 kg sphere only "klunks".

Because of Gibeon’s significance, I thought I’d really go overboard with the text this time – even more than usual! So for those that want to skip it, I’ll briefly comment on the photos before I go into Gibeon’s history.

Photo 1 shows a 50 kg individual, a 4.6 kg 100 mm diameter sphere, and a 180 mm Damascus letter opener fashioned from Gibeon metal (the 1 cm cube in the upper right corner of the image was included to provide an estimate of sizes). Photo 2 provides additional views of the individual to show its regmaglypts, shrapnel-like features, large diameter blowouts, bent and hammered-like deformation, and a channel cut by hot gasses as it became oriented for a time during its fall (both a 1 cm and 1 inch cube are included in this and the next picture to give a better idea of sizes). Photos 3 and 4 provide additional images of some of these features. Photo 5 gives an enlarged view of the front and back side of the letter opener, and to help show how nicely Gibeon’s fine octahedrite structure maps onto the sphere, a 16 second movie is included of it rotating on a turntable.

And now for some history . . .
One of the biggest falls ever, Gibeon likely entered Earth’s atmosphere at a ten to twenty degree angle from a north-westerly direction and subsequently burst into pieces high in the air. Having fallen over southwest Africa in prehistoric times, Gibeon’s strewn field covers an elliptical area approximately 230 miles long and 70 miles wide. No corresponding crater has been identified. Some fragments show similar characteristics to Sikhote-Alins, though ablation features can be significantly different given Gibeon’s fine octahedrite structure compared to Sikhote-Alin’s coarse octahedrite one. Gibeon’s iron-nickel alloy contains significant amounts of cobalt and phosphorus, with radiometric dating defining its crystallization age at approximately 4 billion years.

Gibeon was first discovered by the native Nama people who used pieces to make tools and weapons, at first by cold chiseling and hammering, though much later with smelting. Then in 1836 while traveling north of the Bethany mission station, English captain James Edward Alexander heard stories from the natives of "metal rocks" as large as two feet square located on the east side of the Great Fish River. Although several Dutch colonists had previously ventured northwards along that river, Alexander was the first to publish an account of this journey, mentioning the metal rocks in a 1838 two-volume publication. And while he never saw them in his personal travels, he did manage to obtain a sample that he sent to London, where the respected English chemist John Herschel confirmed its extraterrestrial nature:
The specimen in question weighed 21.79 grains; 3.12 of which were separated, and submitted to a hasty preliminary examination for the detection of nickel, if any, but the quantity proving to [sic] small, the whole of the remainder was operated on in a subsequent trial. The iron was highly malleable and tenacious, and apparently of excellent quality, with a somewhat whiter and more silvery lustre than belongs to the metal in its ordinary state, and apparently little liable to oxidation, qualities which are observed in iron, of what is usually considered undoubted meteoritic origin.

Herschel would continue analyzing the sample, further detailing his analyses in his 1821 "Philosophical Transactions", and again later in his 1833 "Annalen der Chemie". After determining that the proportion of nickel in his sample was 4.61 percent, he concluded:
Thus it appears that the specimen brought home by Capt. Alexander, has equal claim to a meteoritic origin with any of those masses of native nickeliferous iron which have been found in different localities, and to which that origin has, without other evidence, been attributed.

Herschel, from the stories of scattered individuals throughout the area, then became the first to recognize Gibeon’s strewn field and propose possible mechanisms for its scattering:
All those specimens, however, have, so far as I know, been insulated single masses. But what constitutes the peculiar and important feature of the discovery of Capt. Alexander, is the fact stated by him of the occurrence of masses of this native iron in abundance, scattered over a considerable tract of country. If a meteoritic origin be attributed to all these, a shower of iron must have fallen, and as we can imagine no cause for the explosion of a mass of iron, and can hardly conceive a force capable of rending into fragments, a cold block of this very tenacious material, we must of necessity conclude it had to arrive in a state of fusion, and been scattered around by the assistance of the air or otherwise, in a melted, or at least softened state.

In subsequent years Europeans established large cattle ranches in the area and recovered many more large pieces. Sometime in the early 1850s a nearly 180 pound mass was found on a clay plain near the Lion River. John Gibbs subsequently transported it by ox wagon to Cape Town, where the meteorite was purchased by Professor John Tennant, the mineralogist to Queen Victoria. Tennant then sent it to Amherst College in America where Charles Upham Shepard became the first U.S. scientist to analyze a principally intact Gibeon individual. He described his results in his 1853 publication, quoting Gibbs when describing the cut marks on the meteorite:
The part cut has been done by the Namaquas for fabricating arrow-heads and assagais; the traces of two or three abortive attempts of cutting may also be seen on the surface of the mass.

Shepard was also the first to detail the conditions about which a Gibeon meteorite had been found and to estimate its terrestrial age. He described clay given to him from the area around his sample’s resting location as compact and hard marl penetrated by seams of fossil shells replaced by iron pyrite. From that he surmised the meteorite had fallen in the tertiary period – a now largely unused geologic term describing a time spanning from the dinosaurs’ extinction until about three million years ago (though today scientists believe Gibeon’s fall was more likely 200 or so million years ago). And like Herschel, Shepard too inferred a strewn field from the reports of multiple masses.

Four years later a 500 pound example was recovered, and in the first few years of the 1900s several additional large masses were found. One – a 390 pound individual discovered in 1899 near Mukorob – was sent to the Naturalienkabinett state museum in Stuttgart where Emil Cohen and Aristides Brezina (the leading experts on iron meteorites at the time) studied it. In 1902 Cohen and Brezina were able to chemically pair the Mukorob mass with both Gibb’s Lion River and Alexander’s earlier Bethany meteorites, scientifically proving the existence of Herschel’s and Shepard’s previously inferred strewn field.

Then between 1911 and 1913, Dr. P. Marks – Chief Geologist for the Colonial Administration of German South West Africa – thoroughly prospected the area, collecting 37 additional individuals weighing between 400 and 1100 pounds that he subsequently sent to Windhoek for safe keeping. But despite a law defining meteorites as national monuments not to be removed from their natural sites or in any way damaged or destroyed – a law that carried with it a fine of up to 600 German Marks (about $3,600 in today’s dollars) – several were donated to foreign museums and prominent collectors worldwide. Today, after the theft of another few, only 30 of the Windhoek meteorites remain.

Most pieces recognized in the 1800s and early 1900s as meteorites were quite big. As late as the publication of the Handbook of Iron Meteorites in 1975, scientists were still reporting that Gibeon consisted primarily of large masses and lacked the smaller pieces like those found associated with the Canyon Diablo, Odessa, and Sikhote-Alin falls. But it is now known that many of the more obvious smaller fragments had been collected by natives and made into tools and weapons, while the discoveries of other smaller pieces have been aided by the use of modern metal detectors. In all, well over 26 tons of material has been recovered.

Gibeon meteorites exhibit beautiful Widmanstӓtten patterns appreciated both by collectors, jewelry designers, artists, and knife makers. As the meteorite became more sought after, increasing numbers of smaller Gibeons began to be illegally exported, with prices remaining quite low. But the falling availability of Gibeon in more recent years has caused subsequently rising prices, and there have been reports of some vendors misrepresenting as Gibeon the now more common Muonionalusta – an arctic meteorite with very similar Widmanstӓtten patterns, but one that is much more rust-prone than the quite stable Gibeon.
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Steve Brittenham
 6/23/2017 1:13:33 PM
Thanks, Jarkko! You're quite welcome. And John, I almost commented on that in the write-up! The problem is that the sphere is just a bit too big to fit, darn it, and the hole is too irregular and would scratch the sphere. Instead, I have one of the National Geographic Apollo 11 moon landing commemorative sets (with the lander, a rover, and two astronauts) that I "adorn" it with. Sacrilege, I know, but now you more about my personality :).
John Divelbiss
 6/23/2017 12:48:57 PM
the scoop in the 50 kg specimen would make a nice place to display the 4.5 gram sphere...at least for a photo-op.
Paul Swartz
 6/23/2017 10:31:38 AM
I forgot to "publish" the video on youtube, but it's all fixed now:)
Graham
 6/23/2017 5:13:30 AM
Wonderful examples...
Steve Brittenham
 6/23/2017 2:37:32 AM
Hi folks. The video doesn't seem to work, and Paul is on vacation, so I used a friend's account to upload the video onto YouTube (I don't have my own account and have never done this before, but it appears to have worked). Paul doesn't allow URLs, so I can't provide a direct link. But you can go onto YouTube and find it by searching for the following: "rotating gibeon meteorite sphere"
Jarkko Kettunen
 6/23/2017 2:03:04 AM
Beautiful! Thank You for sharing!
 

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