Archive for the ‘My meteorites’ Category

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My meteorites: moldavite (2g)

October 4, 2018

I didn’t even know moldavites existed until last year. One of the highlights of my trip to the 3RF Messier Marathon in the spring of 2017 was seeing Jeff Barton’s meteorite collection. He set it out for us to peruse one day, and it covered a classroom’s worth of tables. I barely knew from meteorites back then–hadn’t caught the bug yet–but a few things stuck in my head. One was his collection of Chelyabinsk meteorites from the 2013 airburst. Another was his collection of tektites. I knew what tektites were in general, but I’d never seen any firsthand. Jeff had a really nice, good-sized moldavite and he encouraged us to hold it up to the light so we could see that it was translucent glass. I got a few snaps of that and I definitely remembered it.

A couple of months later I was driving back from a museum visit in Mesa, Arizona, with a colleague, and we stopped for lunch and gas. There was a rock shop across the street so I thought, “What the heck” and went in. Amongst the other treasures was this little moldavite in a little display case. I checked it out carefully–there is a burgeoning market for fake moldavites, but most are easy to spot as cast glass. All signs point to it being genuine, so I bought it as a souvenir of the trip.

Fifteen million years ago, a massive impact in what is now southern Germany created the Nördlinger Ries crater, which is 24 km (15 miles) across and still up to 150 meters (~500 ft) deep, despite considerable subsequent erosion. The impact scattered showered tektites over a vast area of east-central Europe, including parts of southern Germany, Austria, and the Czech Republic. Moldavites are typically green. They draw their name from the Moldau River in the Czech Republic, where the first pieces to be scientifically described were found.

This moldavite is one of my favorite pieces in my little collection. At outreach events I encourage people to hold it up to the light, and it never fails to impress. It’s strange, but satisfying, to hold a piece of glass 15 million years old.

Before I started reading up on meteorites earlier this year, I assumed that tektites must be pretty common, since they are impact glass from big meteorite impacts, and the Earth has had hundreds or thousands of crater-forming impacts in the last few hundred million years. But most known tektites can be traced to just four impacts:

  • an impact near southeast Asia or Australia, about 780,000 years ago, that produced the Australasian strewnfield (australites, indochinites, rizalites);
  • the Lake Bosumtwi impact in Ghana, about 1 million years ago, that produced the Ivory Coast strewnfield (ivorites);
  • the Nördlinger Ries impact in Germany, about 15 million years ago, that produced the Central European strewnfield (moldavites);
  • the Chesapeake Bay impact on the east coast of North America, about 34 million years ago, that produced a North American strewnfield (bediasites, georgiaites).

There are exceptions:

  • a Central American strewnfield in Belize, with tektites dated to 820,000 years ago, which only started to be reported in the 2010s;
  • Darwin glass, an impact glass associated with the Darwin Crater near the west coast of Tasmania, estimated to be about 810,000 years old;
  • Libyan desert glass from the eastern Sahara, inferred to be the result of an impact or airburst about 26 million years ago (strictly speaking, probably a surface melt rather than melted material thrown through the air).

If you know of a tektite strewnfield or impact glass site that I’ve missed, please let me know in the comments.

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My meteorites: Canyon Diablo

September 29, 2018

I only have a tiny fleck of the Canyon Diablo meteorite that created Meteor Crater in Arizona. And I didn’t even buy it myself–it was a gift from my friend Andy Farke.

I’ve been to Meteor Crater three times, and it’s been an amazing experience each time. In the gift shop, they have these little baggies for a few bucks with an info card and a little chunk of Canyon Diablo. Andy gave me mine years ago, and I bought one for my son, London, on our last visit.

If you’re wondering why the info card says “meteorite oxide”, it’s because the Canyon Diablo meteorite has been on and in the ground for a long time, and it’s had the opportunity to oxidize. Some of the iron oxide is hydrated iron(III) oxide, good old FeO, better known as rust, and I’ve certainly seen a lot of weathered Canyon Diablo specimens with a reddish patina of rust. But much of the iron oxide is iron(II, III) oxide, Fe3O4, better known as magnetite. Magnetite is black or dark gray, and I reckon that’s what I’ve got here, at least on the surface of this bit. I haven’t read enough to know if there might be unoxidized meteoritic iron in the middle, and I’m not going to tumble the specimen to find out!

My little piece of Canyon Diablo doesn’t look like much in the bag, but up close it has a surprising amount of character. I like it. It pays to not get too jaded about a piece of another world, no matter how humble.

Other posts in this series:

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My meteorites: Middlesbrough meteorite (cast)

September 25, 2018

This is the object that fired my interest in meteorites this year. Back in April, I gave a talk about meteorite impacts and mass extinctions at the Alf Museum. I took my little meteorite collection to have some hand specimens to show around afterward. The whole experience got me excited about meteorites, and I started doing some research online.

I don’t remember exactly what investigative chain led me to the Middlesborough meteorite, whether I found the cast on eBay first, or the Wikipedia article about it. Probably the eBay hit first, because it would never have occurred to me to search for it on eBay had I found the Wikipedia article first. Molding and casting of important specimens may be extremely common in my day job of paleontology (even just for fun), but it is not common at all for meteorites. Off the top of my head, I can only think of a handful of meteorite casts I’ve seen: the Middlesborough meteorite; the Stromboli stone, another oriented meteorite; and the flanged, button-shaped Australite tektites. A scale model of the gigantic Willamette meteorite, made available by Nakhla Dog Meteorites, also deserves mention here. I’m sure there must be more out there, but probably not a great many more.

In any case, the Middlesborough meteorite was my first encounter with the phenomenon of oriented meteorites: meteorites that maintained the same orientation as they were melted by their passage through the atmosphere, and came to be shaped like the nose cones or heat shields of spacecraft. Examples range from tiny, button-shaped meteorites 1cm in diameter to large meteorites weighing hundreds of pounds. Most of the best-known oriented meteorites were observed falls that happened during daytime and often in the summer months. I think there’s a very good reason for that: possibly because of their aerodynamic shapes, most oriented meteorites come cooking in at a several hundred miles per hour and bury themselves in the ground at depths from a few inches to a few feet. I assume that oriented meteorites fall just as often in darkness as in daylight, and in winter as in summer, but since most of them bury themselves, the ones that are seen impacting have a much better chance of being discovered, and there are more people out and about to see them in the warm months of the year. Especially in farm country (which statistically has a better chance of collecting meteorites than urban areas because there’s so much more of it), you don’t tend to go around sticking your arm down newly-observed holes in the ground on the off chance that there might be meteorites down there.

I didn’t know all this when I found the cast on eBay, of course. I did some comparing around, decided that the asking price was reasonable, made the purchase, and then set about educating myself about this new (to me) class of objects. Whenever I wrap my head around a new domain of knowledge these days, I like to crystallize what I’ve learned by putting together a slideshow on the topic. These slideshows serve two purposes: they help me remember what I once knew, the next time I circle back to that topic, and they help me introduce others to the subject. I spent a week of evenings reading up on oriented meteorites, made a little slideshow, which I presented at the next PVAA meeting, and then turned the slideshow into a photo book through Shutterfly. You can see the book amidst my expanding meteorite collection in the last post.

I will probably write more about oriented meteorites in the future. For now it is very satisfying to have a cast of the Middlesborough meteorite. I see that I’ve managed to write a whole post and hardly say anything about the history of the meteorite itself, its discovery, and subsequent studies. I’ll try to get to those things in the not-too-distant future.

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Meteorite show-and-tell at the PVAA September meeting

September 22, 2018

Last night was the September general meeting of the Pomona Valley Amateur Astronomers. Instead of having an outside speaker, we had meteorite show-and-tell. Members brought their personal collections of meteorites and impactites, or talked about their history with meteor-hunting, or both.

We kicked off with a short talk by Dr. Eldred Tubbs, who told us about his experiences working with the Prairie Meteorite Network when he was on sabbatical from Harvey Mudd in 1969-1970. The Prairie Meteorite Network was a program run by the Smithsonian Astrophysical Observatory between 1964 and 1975, which used a series of wide-format cameras scattered across the Midwest and Great Plains to capture images of bright meteors, in hopes of locating the resulting meteorites. In ten years of operation, the Prairie Meteorite Network only discovered one meteorite fall, the Lost City meteorite from just outside of Lost City in eastern Oklahoma.

We then proceeded more or less by size of collection. Our club secretary, Ken Elchert, only has one meteorite-related specimen, but it’s a doozy: a massive bilobed indochinite tektite the size of a small pastry. This blob of glass solidified in the atmosphere from molten material blasted out of a huge impact in southeast Asia about 700,000 years ago. I love tektites–externally they resemble black rock, like basalt, but in fact they are glass, so they only weigh about half as much as you might expect when you pick them up. Ken’s specimen, obtained from a gem and mineral show a few years ago, was easily the biggest tektite I’d ever gotten to see firsthand or touch.

Gary Thompson, our club treasurer, was up next. He presented two small meteorite specimens in nice cases. You can see them on the right side of the photo above, surrounded by books. I wasn’t taking careful notes so I don’t remember the details on the second, but the first, in the larger, wooden box, is a piece of an observed fall from 1918 in Russia.

Laura Jaoui was up next. She has an extensive collection of small specimens, including fragments of lunar and Martian meteorites and a couple of small pieces of the Chelyabinsk meteor that exploded over Russia in 2013. Laura also had a lot of cut and etched pieces to show the internal structure of meteorites, especially the beautiful Widmanstätten patterns inside iron meteorites. She had thoughtfully included a variety of magnifying glasses, jewelers’ loupes, and magnets for investigating the structure and properties of the samples in her collection.

I was next up, with my little collection. I haven’t blogged about all of them yet. The Middlesborough meteorite is not the original–that’s on display at the Yorkshire Museum. My copy is a cast that I obtained this spring, which fired my interest in oriented meteorites. I hadn’t known that such things existed, and I spent a few evenings educating myself about them. I put the results of my research into a slideshow, which I gave for the club late this spring, and later turned into the photo book shown here with my meteorites. In the time since I blogged here about my pieces of Campo del Cielo and Sikhote-Alin I’ve obtained additional, smaller representatives of both falls. The NWA Saharan chondrite I got on eBay earlier this year, and the tiny fleck of Canyon Diablo is from the gift shop at Meteor Crater. I picked up the moldavite in the center at a rock shop in Arizona last year. I do intend to blog about all of these things in time.

The anchor of the evening and the star of the show was Jeff Schroeder’s collection. Jeff has been finding, collecting, classifying, and working with meteorites since the 1970s, and he’s worked with some of the pioneering SoCal meteorite hunters. Almost everything on the long table in the above photos is his, and that’s only a fraction of his collection. Jeff gave us a wonderful talk on the history of the collection–much of which is bound for local universities in time–and on the histories of the specimens themselves, and what they tell us about the history of the solar system.

All in all, it was a great evening, with lots of great specimens and inspiring conversations. We should do more things like it in the future. The 50th anniversaries of the Apollo missions are coming up, and we’re planning to have members give short talks about each manned Apollo mission in the month of its 50th anniversary. But we should have a night next year just for people to bring their memorabilia of the space program. We have a lot of retired aerospace engineers in the club, including people who worked on the Apollo missions and the Space Shuttle. It would be great to hear about these things firsthand.

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My meteorites: Sikhote-Alin shrapnel (186g)

April 30, 2018

This is one of my favorite things: a piece of shrapnel from the Sikhote-Alin meteor that exploded over Russia on February 12, 1947. I picked it up at RTMC a couple of years ago.

I love it because it looks exactly like what it is: a wrecked piece of iron, fractured with the rest of its parent body from the core of long-destroyed planetoid, blasted asunder in the atmosphere in a multi-kiloton airburst, and finally shattered against the bedrock of the Sikhote-Alin mountains in far eastern Siberia. Every surface bears witness to the awesome energies of its birth, unleashed in a chain of events that we can barely comprehend, and certainly could not survive.

It fits perfectly in the hand, inviting you to run your thumb over its cracks, pits, and twisted, jagged edges. It has a satisfying heft, befitting a solid chunk of metal. It is 93% iron and 6% nickel, with small amounts of cobalt, phosphorus, and sulfur, and bare hints of germanium, gallium, and iridium. At room temperature it feels cold to the touch, as if it somehow still holds the chill of space.

I like to pass it around and have people handle it. With its weight, seemingly unnatural coolth, and textures that so clearly tell the story of its creation, it’s a fantastic hand specimen. I like to hold it myself, and think about the billions of years it spent in space. It was floating around out there while our ancestors attained multicellularity, backbones, limbs, amniotic sacs, hair, bipedality, fire, agriculture, writing, telescopes, powered flight, and the ability to split the atom. And then our paths crossed, quite literally, when the trajectory of the Sikhote-Alin meteoroid intersected that of Earth.

The energy released by the airburst of the Sikhote-Alin meteor is estimated at 10 kilotons (for comparison, the Chelyabinsk meteor in 2013 was about 500 kilotons). In all the long history of Earth, such large explosions had been the exclusive province of volcanoes and asteroid and comet strikes. But the Sikhote-Alin meteor entered a new world, where its 10-kiloton detonation was only the sixth largest explosion on Earth in the preceding 20 months, behind the atomic blasts at Trinity, Hiroshima, and Nagasaki in 1945, and the Able and Baker tests at Bikini Atoll in 1946 (all between 16 and 23 kilotons).

It is hard to think about such things, so removed from us in time, and from the scale of our experiences. I hold this cold piece of sharp-edged iron and think about all of the other Sikhote-Alins, Chelyabinsks, Tunguskas, and Chicxulubs out there, any of which might cross our path at any moment, and some of which inevitably will. In the words of the astronomer Kevin Zahnle (quoted in Seeing in the Dark by Timothy Ferris), “a day will surely come when the sheltering sky is torn apart with a power that beggars the imagination.”

Because it is only a matter of time until Earth is threatened with a civilization-ending or mass-extinction-level impact, is is also only a matter of time until we stop thinking of astronomy as the niche preoccupation of a few, and start realizing that it is an unavoidable aspect of our survival.

We need reminders of that fact. This one is mine.

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My meteorites: Campo del Cielo (40g)

April 25, 2018

My recent talk on impacts and the end-Cretaceous extinctions reminded me that I’ve never posted about my meteorite collection. It’s not a large collection, just a handful of things I’ve picked up, but each is satisfying in its own way.

This is the first meteorite I ever owned, a 40g piece of Campo del Cielo from Argentina. It’s about the size of the last joint of your index finger. Following the universal standard for meteorite photography, the scale cube in the photos is 1cm.

I picked this up probably 15 years ago at an auction at a Society of Vertebrate Paleontology annual meeting. I don’t remember the year – early 2000s for sure. The meteorite came with a little drawstring bag made of red felt, and a certificate of authenticity. It was clearly marked as a chunk of Campo del Cielo, which fell over northwest Argentina four or five thousand years ago.

The original Campo del Cielo meteor exploded in the atmosphere, much like the Chelyabinsk meteor over Russia in 2013, but on a much grander scale. The Chelyabinsk meteor is estimated to have been 20m in diameter, and it produced an airburst of approximately 500 kilotons. The Campo del Cielo meteor was probably more like 50m in diameter, so it would have been a multi-megaton explosion in the upper atmosphere. The resulting strewn field is 2 miles wide, more than 11 miles long, and includes at least 26 craters with diameters of up to 100 meters; the impact of the fragment that produced the 100-meter crater would itself have been multi-kiloton event.

I didn’t know any of that at the time I got the meteorite at the auction. I vividly remember how much I paid for it: $80. I remember so clearly because I almost instantly regretted it. I don’t know who I was talking to afterward, but someone looked at the meteorite and commented that it would be easy to fake with a bit of iron slag. That seemed plausible – it didn’t look like any meteorite I’d seen pictures of, so I assumed the chance that it was a fake was high. I had other fish to fry at the time, being a new dad and halfway through a dissertation, so I never did any research to see if the meteorite was real or fake. I kept it, but I never put it on display, and over the years I sort of lost track of it.

I rediscovered it this January during a major bout of house-cleaning. It’s funny, in the time between when I obtained this piece and now, I’ve looked at so many meteorite photos that I can just glance at this and think, “Yep, it’s a Campo”. Five minutes of image searching for Campo del Cielo pieces will turn up many authenticated examples with the same general appearance, like angular chewed gum with fracture lines and surface pitting. Campo del Cielo is one of the least expensive meteorites to obtain, with prices around $1/gram still being pretty common. (So in fact I overpaid a bit back when I got this, but since it was an auction to support the society I don’t mind.) With such distinctive morphology and such low prices, it’s probably much less expensive to simply buy a real piece of Campo than to fake one, especially at small sizes.

So even though it is one of the smallest pieces in my collection, this little gem means a lot to me. It tells two stories: one about my personal journey from interested-but-ignorant space enthusiast to semi-knowledgeable, semi-professional astronomy writer – and one about a 65,000-ton chunk of iron from the core of a shattered planetoid, which exploded with the force of an entire nuclear arsenal and showered a vast area with what must have been a lethal rain of shrapnel, from pea-sized up to house-sized. Including this little piece, cosmic voyager and witness to awesome forces of creation and destruction.

– – – – – – – – – – – – – – –

If you’re interested in obtaining a meteorite or starting a collection, I have two pieces of advice. The first is, buy from reputable dealers. Many honest dealers are members of the International Meteorite Collections Association and will list their IMCA member number wherever they do business. There are good dealers who are not IMCA members for various reasons – some just don’t like clubs and the politics that sometimes comes along with membership – but it’s a start. Also check seller feedback if you buy from online markets like eBay. And use search tools to do quick checks on individual dealers; the meteorite collecting community is pretty vigilant about detecting and outing bad actors.

The second and probably more important guideline is to educate yourself. Spend a week of evenings looking through websites and online ads and learning to know what to look for in genuine meteors. It’s not completely foolproof – a few unscrupulous people will pick up bits of inexpensive recent falls and try to pass them off as examples of rare and valuable historical meteorites, for example – but at least you’ll develop the knowledge to tell genuine meteorites from “meteorwrongs”. Good hunting!

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A little piece of Mars

July 21, 2016

Mini Museum no 3614 DSCN1469

This is my Mini Museum: a collection of tiny samples of rare and interesting specimens from the history and prehistory of Earth and the solar system. There’s a lot of stuff in here that is very satisfying as both a paleontologist and an amateur astronomer. Highlights for me are the preserved woolly mammoth meat, the fiberglass casts of Diplodocus bones used as the Krayt Dragon skeleton in Star Wars: A New Hope, and, above all, the tiny piece of the Martian meteorite Zagami. It’s labeled “Martian atmosphere” because the meteor is known to contain tiny bubbles of Martian atmosphere in pockets of melted glass (Marti et al., 1995).

The specimens are embedded in a single block of acrylic that is 5 inches tall, 4 inches wide, and 1 inch thick. At $299 it’s not cheap, but it’s a pretty astounding collection of objects at any price. There is also a smaller, 10-specimen edition for $99. It doesn’t include Zagami or the Krayt Dragon, but it does have asteroid fragments, Stegosaurus plate, woolly mammoth meat, fulgurite, and the moon tree sample. These will sell out at some point, so if you’re interested in picking one up, don’t tarry.

Reference

Marti, K., Kim, J.S., Thakur, A.N., McCoy, T.J. and Keil, K., 1995. Signatures of the Martian atmopshere in glass of the Zagami meteorite. Science, 267(5206), p.1981.