Pallasite Meteorite

[CMD]

For the layman and collectors alike, the meteorites known as pallasites, are admired for their sheer beauty. Don't have to be a student of meteorites to like a slice of Pallasite   This particular slice would not even be considered a prime specimen. It's not sliced thin enough to be translucent for one thing. And the peridot crystals, set in a nickel-iron matrix, are not really gem quality. But it's a pretty gift from space nonetheless. Imilac is the name given to this meteorite find from the Atacama Desert of Chile. As a Pallasite, Imilac is a stony-iron meteorite, the other two main types of meteorites being stony and irons.


Here's Imilac in the form of a small fragment in which a "window" has been polished to reveal the structure of olivine in a nickel-iron matrix.



Imilac. Peridot in nickel-iron.

[JoshinMO]

OOH! :woohoo:

[painshill]

Very nice Charlie. Pallasites are my favourite meteorites.
There are only 100 classified examples but several of them were very large falls so it’s possible to get a nice example at a reasonable price. We don’t know for sure where they originated, but their composition is typical of the core-mantle boundary of an asteroidal body that was large enough to have differentiated into something with a metallic core. The variation in composition suggests that there may have been at least three different parent bodies which may have formed during glancing impacts between Moon-to-Mars-sized protoplanets in the early solar system.
Here’s a few more:
Polished slice of Brahin, found in 1810 - Belarus, Russia.

… and a chunkier specimen of Brahin.

Pallasovka, found in 1990 - Volvogradskaya, Russia

Jepara, found in 2008 – Java, Indonesia.

Seymchan (anomalous), found in 1967 – Magadanskaya, Russia

Brenham (anomalous), found in 1822 - Kiowa County, Kansas

Huckitta, found in 1924 - Arapunya Station, Australia

Admire, found in 1881 - Lyon County, Kansas, USA

  And here’s an interesting one:

On 1st February 1956 at 03:30 Ural Time (Russia), a fireball shining brighter than the sun and leaving a smoke trail was observed by numerous eyewitnesses in an area of about 500 square kilometres across Russia. The fireball disappeared in 5-6 seconds but the trail was visible for an hour. Windows in nearby villages were broken by the shock wave. A meteorite reportedly fell on the frozen Shirokovsky reservoir, situated on the Kosva River near Shirokovsky village, producing a 42 cm diameter hole in 80 cm thick ice. Magnetic particles enriched in Nickel were extracted from the ice surrounding the hole. Several attempts by divers to recover the meteorite from the bottom of the reservoir were unsuccessful. In early 2002, anonymous searchers found many fragments of iron-rich material, totalling around 150 kg, at the site.
Specimens from the recovery soon appeared on the collector market (at extremely high prices) and claimed to be from a pallasite meteorite. It certainly looks like one, but the Meteoritical Society ultimately issued a “special statement” refuting these claims. Based on extensive testing, it was concluded that the “Shirokovsky pallasite” specimens were “probably not meteorites” and that “the petrology and geochemistry of this object strongly suggest that it has a terrestrial origin.” It is currently classified as a “pseudometeorite” in the database, although the Society stopped short of using the word “fake”.
In 2005, Dransart -and- Guérin investigated the material in more detail and attempted to replicate it using metallurgical processes. They concluded that it had likely been man-made by a process known as “sintering” - a high-tech process used to manufacture things like turbine blades, bearings, brake pads and hydraulic parts for aircraft. Atomization of finely powdered metal by heating in an oxygen-free gas environment produces high strength solid metallic objects without raising the temperature above liquefaction point. It can’t have been cast from molten metal because that would have needed to have been dome in zero-gravity conditions to prevent the lower-density olivine components from “floating” to the surface of the molten metal. I acquired that specimen cheaply, in the wake of the “meteorite” being discredited.
A. Alexeyevich, a member of the Russian Geographical Society and a participant in the search expedition asserts that thirty people, not counting the local volunteers and Shirokovsky Power Station staff, participated in four search expeditions between 2000 and 2003. He has challenged the findings, citing eye-witness evidence and potential errors in the analytical assessments. He claims it is “almost certain” that what his divers lifted from the reservoir bottom is what fell from the sky, broke through the ice and left the iron nickel traces in 1956, simply because there was nothing else found on the reservoir bottom that could have left such traces. He expects that new test results will show either that the shifting of isotopic ratio relative to the line of terrestrial rocks was due to poor preparation of the samples or that Shirokovsy will ultimately be assigned to the anomalous group of  lunar, Martian, aubrite meteorites etc.
He also points out that if it had been man-made by sintering then it must have been produced within a mould. Since some of the specimens have protrusions that jut out opposing angles, it’s difficult to imagine how the item could have been extracted from a mould without breakage. If it is a fake (which would be my belief) then someone went to an awful lot of trouble to produce it.

[rmartin]

Great thread Charlie and some amazing pics. Thanks for the additional info Roger. Got my eye out for one of those!

[CMD]

Better photo of 93.5 gm. Imilac part slice.

Thank you, Roger, for all the other information and photos. I believe I only have one other Pallasite, having always strongly favored stone meteorites. Time to figure out what to do with the collection, and, as a result, I'm seeing pieces I have not seen in years.

[CMD]

Great stuff, Roger. I've been waiting to see the photos while you worked on that informative comment. That Jepara is most unusual looking. And I see it's a relatively recent find. Very attractive and different looking! I've been away from the hobby and have never heard of or seen that beauty before today! Good knowing someone like yourself can correct my errors, (and I'm rusty, having not actively collected in quite a few years), and add so much more to boot. I may use this category to post space rocks now and then.  Ultimately, I hope to create a website to display the collection. Unfortunately, it has to go, and as I go through it these days, my interest and love is reawakened, and oh, no, how do I sell it :rolf:
Thanks for all those photos. Not hard to understand why the Pallasites are your favorite. And those are superb examples of those varied locations.

[CMD]

It terms of recovery, meteorites are either witness falls, or finds. The latter are found without ever having been seen to fall, and the former are often recovered after witness reports from a broad area are triangulated. You use those reports to pinpoint where the search for surviving pieces should be focused.
This is Marjalahti, a witness fall Pallasite that fell in India on June 1, 1902. People prefer translucent slices where Pallasites are concerned, for obvious reasons....

[painshill]

As Charlie said, the greenish-yellow mineral in pallasites is olivine, which – as the distinctly green magnesium-rich variety forsterite - is given the non-geological term “peridot” when it is of gem quality. Olivine from meteorites is rarely of that quality in crystals which are large enough to yield decent gemstones. It’s not usually a good green, frequently has inclusions or impurities and habitually has shockwave cracks running through it (making it prone to splitting during or after cutting). There are however some exceptions… notably the Esquel meteorite from Argentina, which does occasionally contain sizeable pieces of gem quality material that can be cut. This is still the largest one I believe… a whopping great 1.5ct:

I believe this picture is from Robert Haag (“Meteorite Man”) and that he still owns this specimen.
The meteorite was found in 1951 by a farmer digging a hole for a water tank. It’s not clear exactly what the original weight was and some pieces may have already been sold, but Haag purchased the remaining mass of 680 kilogrammes in 1992.

[CMD]

Haag carved out quite a legacy in the history of meteorite collecting. As Roger can attest, the relationship among collectors, hunters, museum collection curators, and meteorite scientists is much more symbiotic then the relationship between archaeologists and artifact hunters/collectors. Nonetheless, in a meteoriticist's perfect world, all meteorites would be recovered by and curated by scientists, not collectors. That's the case in Antarctica, where meteorites collect on the ice. That icy continent is a treasure trove of rocks from space. But so are some hot desert environs, and the Sahara region of Northwest Africa has been a treasure trove for collectors and scientists alike.
Here's a photo from his catalog showing Haag with a 37 ton specimen of the Campo del Cielo iron meteorite from Argentina. Haag bought it from someone who didn't own it, and it remains in Argentina. I was lucky to get several nice meteorites from Haag back in the days when there were far fewer collectors then at present.

http://www.meteoritemarket.com/CCinfo.htm