Meteorite Times Magazine
Contents Paul Harris
Featured Articles
Accretion Desk by Martin Horejsi Jim’s Fragments by Jim Tobin Meteorite Market Trends by Michael Blood Bob’s Findings by Robert Verish Micro Visions by John Kashuba Norm’s Tektite Teasers by Norm Lehrman Mr. Monning’s Collection by Anne Black IMCA Insights by The IMCA Team Meteorite of the Month by Editor Tektite of the Month by Editor
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The Chiang Khan Meteorite Fall: A Gift That Just Keeps Giving Martin Horejsi
At 5:30 in the morning on November 17, 1981, a fireball exploded high above the citizens Ban Klang and Chiang-Khan in the province of Loei in Thailand. Loud thunderous reports rolled across the land right before a shower of stones pelted the landscape.
My pleasantly oriented individual of Chiang-Kahn sits atop a one-cm cube facing away from the center of the earth.
Scientists arrived on scene several days after the locals had gathered up all the easy-to-find pieces that amounted to about a third of a kilo in the form of 31 separate pieces with the largest at 51 gram.
A couple weeks later another piece was found but that one weighed more than twice that of all the previous material amounted. So with the additional 800g individual, the total known weight of Chiang-Khan unofficially broke the one kilogram mark. Oddly, the TKW of this H6 chondrite is usually reported as 367 grams, or as the initial amount found shortly after the fall.
But the TKW story continues. In 2000, a fellow named Oliver Alge mounted a week-long expedition to the strewnfield. That week turned into several months. Oliver recounts his story online and in a paper that accompanied many of the specimens that he sold as part of fund-raising effort. More on that effort is available on Oliver’s website.
Fund raising with meteorites is not a new thing but is relatively rare. I wrote about my experience with what I called “Bakesale Juanchings” or small individauls from that famous fall that were collected by students and teachers, then brought to America to be sold at the Tucson show. I was lucky to play a small part in that event buy buying their stones, and then selling them to recover my cost since my money was already headed back to the schools in China. Here’s some info on that from a previous Meteorite Times article.
This is a excerpt of Oliver’s Chiang-Kahn story as described on his website.
“Due to the political circumstances prevailing in Laos at that time, there are hardly any testimonies about this meteorite fall from there. My Chiang-Khan expedition 2000 was initially intended to last one week only, but actually I spent the whole time from November till the end of February 2001 (and again 6 month) in the strewnfield and was able to shed some light into this darkness.
I met a Laotian army officer who, right after the fall, was entrusted by the government with the task of seizing all fallen stones from the locals (threatening people with punishment!), in order to hand these specimens over to the authorities in Vientiane. People were told that this was dangerous Thai material. Subsequently, the specimens are said to have been sold to the Soviets.’
A oriented meteorite shows the earth only one side during it’s fall. The crust of this Chiang-Khan individual is mostly intact and contraction cracks are visible.
“About half of the persons I interrogated declared a fall direction opposed to the one officially published: according to them, the fireball traveled southwards, to Thailand, coming from the North (Laos). With Thai observers, this variant of the reports is easy to explain: The tense political situation of those days induced the population to conclude that Laos had fired missiles against Thai territory during the night. Due to the time of the fall, hardly anybody will have witnessed the event visually; the enormous explosion jerked people from their sleep and then engendered this story as their first thought.
I personally convinced myself at 5.30 AM in Ban Klang that except for a few dozen dogs sleeping in the streets, no more than a handful of people could have experienced this natural spectacle. Such fall reports by Laotians, on the other hand, can only be explained by yet another meteorite fall. The aforesaid Laotian army officer saw the fireball coming from the North. He was on night watch in Bagmee when, at about 3 AM, he saw the fireball detonate at an angle of some 45 degrees to the observer. Almost all reports from Laos contain a different fall time and a North-South motion.” Even as an H6, there are still small chondrules that poked their little spherical head up during reentry. The tiny round bumps make viewing Chiang-Khan under magnification much more interesting.
“A Thai fisherman gave a further fascinating account: at said time, he was on the Mekhong river, where he had cast his net to gather some fish for breakfast. He beheld the “devil’s ball” coming from South, and soon it vanished with a mighty burst. He had to seek shelter against the falling stones under a wool blanket, and the pieces that, in quest of a new home, were laying siege to his boat filled both his hands. Afterwards, he said, he had thrown “the ugly black stones”, which for sure meant no good, into the river.” For the serious meteorite enthusiast, the trailing edge of an oriented meteorite can be as interesting as the leading edge, sometimes even more so. Still, the cone or bullet-shaped front end is what really makes a valuable orientated specimen. And Chiang-Kahn does not disappoint.
“Nobody was able anymore to give precise indications as to the exact date of the event. Some 20 years ago it was, so they say, in the month of November, without doubt – that’s what I was told in the villages of the strewnfield. Whatever it was that happened then – one is led to presume a second meteorite fall on the same day or on the day after. According to recent research (isotope analysis), the two large specimens, which are in private Collection and in Chulalongkorn University, Bangkok, do not originate from the Chiang-Khan fall. They are believed to have been transported into Thailand from Laos. Two small pieces from Thailand were analyzed, one is H4 tending to H5; one was determined to be H5 in Japan, whereas the large pieces are H6. Most of all, the noble gas contents of the large specimens differ extremely from those of the Chiang-Khan pieces!”
Thank you again Oliver for working in the field of Chiang Kahn in order to share the story with us, for this is how meteorite history is made.
Until next time…. Meteorite Times Magazine
Summertime Funtime James Tobin
Well summer is nearly over as I write this. It has been a fun season this year. Got in a couple trip to the desert for astrophotography. Got some ceramic pieces made and with both those interests tried new equipment and techniques. I try to never stop learning new things. This article has frankly been a problem. I have been so busy building Canon camera coolers and electronic focuser attachments and other things for my star imaging that I have only been doing routine work with meteorites. Normal cleaning and cutting and diamond lapping. I have not been cutting into anything knew to find exciting unseen treasures. But I am waiting to hear back any time about three very cool stones that are out for classification. I admit to being like a little kid when it comes to waiting for laboratory work. I treat it like Christmas Day. I know there is a big reveal in the future when the results come back and it will either validate the personal guesses I have made about the stones or surprise me in a wonderful way perhaps. I found a few months ago a very friable stone while cutting some mixed up boxes of NWA material. It had a thick layer on the outside that was very crumbly bu,t it was full of wonderful chondrules some of which were quite large. I had to cut several slices to get into the heart of the stone and away from the outside that was falling apart. Here is one of the outer slices that was starting to get better. It is one of the stone I am waiting to hear the results on.
I usually take a thin slice from the stones as I am making the samples to send off for classification. The thin slice goes to my lab in the garage and becomes a thin section which I examine while waiting on the real results. I have never sent just anything off for classification. It has always been the more special stones. But in the future I may begin sending off some the more ordinary material if labs will accept it.
I have described the process of making the thin sections in the past. It is for me a hand made deal. I use a powered diamond lap for the first part but after the material is starting to get thin I go to all by hand grinding. It takes a while and there are a lot of stops to place the slide in my polarized light viewer. But eventually I get to somewhere very close to 30 microns. I made a few thin sections this summer. They will find their way to the camera in the future to get imaged.
I just love all kinds of meteorites but have to admit I have a real soft spot for chondrule rich type 3 and 4 ordinary chondrites. I am just fascinated by the way they look as thin sections in polarized light under a microscope. When I was young I got involved in commercial macro photography. I did work for a group of local commercial artists and advertising firms shooting all their small products for print ads. I was struggling as a young man on my own to make ends meet and the extra money was really welcome. It was great training and today I still love getting in super close on my meteorites and finding out what is there to capture photographically. Seems like all my hobbies and interests find their way back to meteorites sooner or later. My ceramic art is made with meteorite dust mixed into the clay. I am playing currently with some exciting new projects that I hope will actually resemble meteorite slices when the mosaic tiles are done. My gold and silver jewelry work has been including more pieces of meteorite as time goes on. This is the third level of experimentation for my artistic vision of meteorites in clay. I have made thousands of tiny artificial chondrules with about ten different mixtures and colors. I am about ready to try a real mosaic.
So does all this mean that I am obsessed with meteorites and need to find a program. Well maybe. But as far as I no there is no program like MA (meteorites anonymous). Maybe there should be.
If things go as currently planned I will get some meteorite hunting in later in the year. Has been a few months since I did any of that. So far retirement has been anything but rest for me. I have been doing stuff everyday that I had no time for while I was working and that for me is the best. I can spend a few days on each thing I love, and mix meteorites into most of them and work on astro images at night.
There is a Gold Basin Anniversary celebration coming up and going is on my short list of things I want to do. I have been thinking it is pretty dark out there I could take along some stuff and maybe catch some astrophotos at night out there. That is another mix I have not done for a while. Star images from a strewnfield is sounding cooler every time I think about it. If I don’t find any meteorites during the day there is always the chance I will get some good images at night.
I guess at some point I will have to reign in these hobbies and just pick a couple, but for right now I am enjoying being all over the place with them. They all stay fresh since I don’t do any of them all the time.
I know there was not a lot of substance in this article. Summer just does not seem like the time to be really serious and scholarly. So I apologize for the glimpse into my daily retirement life. Promise the next article will have depth and information.
But now it is time to go and empty the kiln. Bye Meteorite Times Magazine
Bob’s Bulletin – Vol. 1 No. 3 Robert Verish
A newsletter for “orphaned” meteorites from the USA.
In my first Bulletin, I introduced the phrase “orphaned-meteorites from the USA”. I defined these “orphans” as being unwitnessed-fall Ordinary Chondrite (OC) meteorite “finds” that are recovered in the U.S.
Unfortunately, the vast majority of U.S. finds are of this type. I went on to write that these U.S. finds were being orphaned from the family of “approved” meteorites for the following reasons:
1) The lack of funding for U.S. researchers to authenticate, classify, and document/record these U.S. OC finds has resulted in several new [negative]; trends.
2) The increasing trend of commercializing the classifying of meteorites by U.S. researchers has priced U.S. OC finds out of the market, and
3) The increasing trend of U.S. researchers to turn away OC finds, even when finders of U.S. OC meteorites are willing to pay for their classification.
In my 2nd Bulletin, I went into more detail about why I use the phrase “orphaned-meteorites from the USA”. I focused on the lack of U.S.-tax-dollar-funding and why no funding was going towards the classification of these particular meteorites. In hindsight, I now realize that I should have pointed-out that there is also a lack of funding for just authenticating and recording that a U.S. meteorite has been found. This function should never be confused with “classifying” a meteorite, which is obviously way more labor intensive and costly.
My point is this: if you already have dedicated U.S. researchers (who have been approved for classifying meteorites) and they are already having U.S. meteorite finds being brought to them, and they are already deciding (visually) whether the find is an OC (and consequently, whether they will agree to classify the find), then why not take one more additional step and record this find and have that data entered into some sort of U.S. OC database? Is it because there are no funds allocated to do this function? Or worse, it actually is funded, but for some bureaucratic reason this function has been deemed “not important”?
[Yes, I know about “provisional” meteorites, but those are a separate issue. For starters, they are: 1) ONLY numbers that 2) STILL have to be formally assigned to pre-classified (and often unauthenticated) rocks that are 3) ONLY from DCAs (Dense Collection Areas). But DCAs can 4) ONLY be assigned after two or more meteorites have already been formally approved by the MetSoc (meteoritical Society) NomCom (Nomenclature Committee). But what I am suggesting is much less involved, and although it may have to be done outside of MetSoc, it still could be done by volunteers for U.S. OC finds.]
A simple question that is often asked is, “How many of these ‘orphaned’ meteorites are there?” But, now you see why this question is so difficult to answer. We simply don’t know.
So, in order for me to do my part to bring attention to this ongoing and growing problem, I will continue to gather data, and along with others, make a list of what we know to be “orphaned meteorites”. To that end, in this newsletter-format, I’m introducing the next five “orphaned” U.S. meteorite finds:
Newsletter for Orphaned Meteorites from USA – Volume 1 No. 3 — September 2015
Meteorite-Recovery Information Petrographic Descriptions Meteorite Specimen Petrographic Descriptions: N140531A N140531B N140531C N150814D N150814E
Example Petrographic Description
Field ID Number N140531A Newsletter 01-3 Location Nevada, USA Thin-section ID Number VTBD Dimensions 3.5cm x 2.5cm x 2cm Weight 30.05 grams Type Specimen 6.4gram endcut – plus thin-section Class Ordinary Chondrite (quite possibly an LL6)
The above example is one way in which I can bring attention to what I predict will be an increasing number of unclassified meteorites found here in the USA. Hopefully, attention will be drawn to what I see as a growing problem, and maybe some institution will offer to help get some of these orphans classified and cataloged.
A newsletter for “orphaned” meteorites from the USA.
References:
Meteoritical Bulletin: the search results for all provisional meteorites found in “USA” – Published by Meteoritical Society – Meteoritical Bulletin, Database. Meteorites of California the list of formally-recognized California meteorite falls and finds.
My previous articles can be found *HERE*
For for more information, please contact me by email: Bolide*chaser
Meteorite Times Magazine
Micro Visions 3.00 John Kashuba
3.00 is a rarely given petrologic grade assigned to meteorites which experienced the lowest levels of thermal alteration on the parent body. (Aqueous alteration is another matter.) NWA 8276 L3.00 was assigned this grade based on laboratory tests and a study by Grossman and Brearley published in 2005.
Among many findings the study’s authors showed that at the onset of thermal metamorphism the average chromium content of iron rich olivine grains in chondrules was relatively high. As metamorphism proceeded those levels receded. And, at the same time, the variance among the values making up those averages changed – starting with a narrow variance, widening then narrowing again with advancing metamorphism.
Combining these two characteristics, Grossman and Brearley presented a scheme for classification of very low petrologic grade chondrites. See this graphically on Grossman and Brearley (2005) page 113, Fig. 15. These characteristics and hence the method has the advantage of being resistant to the effects of parent body aqueous alteration and terrestrial weathering.
The paper presents numerous other thermal metamorphism correlated phenomena including changes in core to rim Cr zoning in ferroan olivine grains, the development of distinct chromite inclusions, the migration of troilite and the expulsion of sulfur from fine chondrite matrix.
Most of this is invisible to our optical microscope but we are still able to enjoy this near-pristine meteorite in thin section. One centimeter square polished surface. Packed chondrules and dark matrix. Incident light. NWA 8276 L3.00 Metal in and around a chondrule. Field of view is 3 mm wide. Incident light. NWA 8276 L3.00 A small metal-layered chondrule. Field of view is 3 mm wide. Incident light. NWA 8276 L3.00 Radial pyroxene chondrule with bleached rim indicative of parent body aqueous alteration. FOV = 3 mm wide. Incident light. NWA 8276 L3.00 Same RP chondrule in partially crossed-polarized light. FOV = 3 mm wide. NWA 8276 L3.00 Edge of the same altered RP chondrule in XPL. FOV = 0.3 mm wide. NWA 8276 L3.00 Overview in XPL showing that many chondrules are porphyritic olivine pyroxene chondrules. FOV = 8.6 mm wide. NWA 8276 L3.00 POP chondrule in XPL. FOV = 3 mm wide. NWA 8276 L3.00 POP chondrule in XPL. FOV = 3 mm wide. NWA 8276 L3.00 Polysomatic barred olivine chondrule in XPL. FOV = 3 mm wide. NWA 8276 L3.00 Barred olivine chondrule in XPL. FOV = 3 mm wide. NWA 8276 L3.00 Same barred olivine chondrule in plane-polarized light. No devitrification of the glass between bars is apparent. If the glass had started to crystallize we might have seen fine needles extending from bars into the glass between them. FOV = 0.3 mm wide. NWA 8276 L3.00 Same barred olivine chondrule in XPL. The space between the bars is dark attesting to its glassy state. The softly defined violet zones are places where the bars do not occupy the entire thickness of the thin section sample. The FOV = 0.3 mm wide. NWA 8276 L3.00 Norm’s Tektite Teasers: Pseudotektites , a Tektite Teaser indeed! by Norm Lehrman (www.TektiteSource.com)
There is a family of remarkably similar (and usually controversial) natural glasses, including, Saffordites (aka” Arizonaites”)Colombianites, Healdsburgites, and Philippine Amerikanites, which I term “pseudotektites”. Placed side by side with the real thing, these look very much like tektites, but they almost certainly are not. We are often approached by individuals that are convinced that they have discovered new tektites or strewnfields. Mostly, the claims can be readily dismissed, but the best- looking ones (pictured below), force us to critically review our tektite recognition criteria.
If those of us who know what tektites are should be asked to describe them to someone unfamiliar with them, I suspect all would include things like dimpled skin, aerodynamic shapes, composed of glass, black or green, not gray. There’s more, but these are prominent descriptors. However, the pseudotektites discussed in this article pose some challenges:
Their skin ornamentation---dimpling, pitting, grooving is effectively indiscernible from that of true tektites. Their transmitted light color is often a smoky- lavender, not a color used in our definition. Tektite-like morphologies are fairly common in the pseudotektites, particularly patties, biscuits, spheroids, and occasionally, teardrops (pictured below).
Assuming that we are correct that these stones under discussion are truly not tektites (and I am quite sure of that fact), then we must devaluate the diagnostic usefulness of the most visually obvious features of a tektite: skin-ornamentation, aerodynamic morphology, and basic dark glass composition. These are not peculiar to tektites.
In searching for characteristics not requiring a laboratory that truly are (or are not) fundamental to the nature of a tektite, I have narrowed my observations to two key negative discriminants.
1) Gray transmitted light color and/or deflection of a delicately suspended magnet indicates the presence of crystalline magnetite. Tektites are given birth in a monstrous plasma fireball. It is true and is probably a direct consequence of formation, that tektite glass is of extremely high purity, devoid of volatiles, and all constituent elements are fully dissolved in the glass. There are never any primary crystallites at all. 2) Internal flow-bands or schlieren, when present, are invariably cut by the morphological surface in pseudotektites. Tektites (when unbroken) are complete primary bodies. Any internal fabric will conform with its bounding morphological surface. The teardrop-morphology Saffordite pictured below is by this criterion recognized as not being a primary aerodynamic form, but is rather an accidental erosional/corrosional similitude of a teardrop that is not complete, but is a remnant of what was once a very much larger primary (volcanic) domain.
The “morphologically-truncated banding” is a valuable recognition tool. A splashform tektite is a complete three-dimensional body, a flying blob of molten glass enclosed entirely within itself. Every viscous taffy-like internal band will honor the ultimate external bounding surface of the shape. Consider a volcanic flow-dome complex composed all or in part of obsidian. Flow-banded domains may extend for meters or even tens of meters. Now, in your mind, let that body chaotically fracture in the accumulated trauma of deep time and let advancing fronts of hydration, devitrification, and other forms of erosion eat into these fracture faces until only a few “buttons” remain in the most central hearts of the boulders. What would they look like? My answer? Saffordites, Healsdsburgites, Colombianites, and (I think) Amerikanites.
(There is something of a scientific mystery hidden in the “Amerikanite” heading:. In my introductory photo, you will take note of an “Amerikanite” from the Philippines. H. Otley Beyer, father of Philippinites, routinely included in his specimen collecting inventories a heading entitled “Amerikanites”, and it is clear from his usage that he was referring to pebbles of terrestrial obsidian that he recognized as masquerading as Philippine tektites. Beyer, to my knowledge, never explains or defines an “Amerikanite” in print. But I am willing to bet that it is a sibling of Safforfdites, Healdsburgites, and Colombianites! The one example in our collection fits nicely on that shelf). These weirdities have a story of their own!
So what are pseudotektites if they are not tektites?
I believe these to represent the final skeletal traces of either very old obsidian or glass that was chemically unstable in its weathering environment.
All glass is geologically metastable and does hydrate, devitrify and recompose (a new word, I think, but they do not strictly decompose, but rather transform from an amorphous state into a crystalline substance, essentially the opposite of decompose, hence, “recompose”) into clays over a few tens of millions of years. Logically, the last bits of remnant glass, geological moments from obliteration and oblivion, must have a corroded and etched skeletal appearance. They truly are quite magical objects in their own right.
These are the most ancient grandfathers of their species and when they are gone their ancestral rock will be extinct. We humans have belatedly learned to care about the passing of biological species in our spaceship ecosystem, but we forget that even the mountains and rocks pass through their natural life cycles and are banished into time past.
These pseudotektites are the final survivors of their ancestral volcanic parents in the geologic Garden of Eden. As the strongest bits in the hearts of boulders, they are something of a crowning gem (---and the gemmy transparent lilac ones do indeed facet into spectacular jewels!). Hold one and marvel. It is not a tektite. It doesn’t need to be. It is a stone with its own amazing story. It is one of the final generation of its kind before ultimate extinction. A grandfather boulder-heart!
A gem Colombianite! Meteorite Times Magazine
Understanding the Early Solar System through the Analysis of Meteorites: The Process of Maximizing Data while Minimizing Sample Destruction Ellen J. Crapster-Pregont
Ellen J. Crapster-Pregont1,2
1.Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, 10964, USA. 2.Dept. of Earth and Planetary Science, American Museum of Natural History, New York, NY, 10024, USA.
Every year approximately 40,000 meteorites make it to Earth’s surface. This value is based on camera network meteor data (Halliday et al., 1989; Bland, 2005) and weathering studies of hot desert meteorites (Bland et al., 1996a,b; Bland, 2005) for stones ranging from 10 to 106 g in mass. Of these, less than 10% are greater than 1 kg and less than 1% are collected, classified, and named (Fig. 1; based on values in Bland (2005) and the Meteoritical Society Bulletin Database). This small percentage is affected by our inability to retrieve many samples, such as ocean falls, and by surface survival rates. Figure 1 breaks down this small percentage a step further to highlight how valuable chondrites, or meteorites from undifferentiated parent bodies, are considering the information they hold about the highest temperature chemistry and processes in the protoplanetary disk as it started cooling and condensing, transitioning from gas and dust to crystalline solids, particularly the refractory (i.e. formed at high temperature) components observed in chondrites such as calcium- and aluminum-rich inclusions. These components preserve the most primitive information about our early solar system, and, as Figure 1 implies, only a small percent of a small percent of collected and classified meteorites contain this valuable information.
One of the greatest goals of a planetary scientist is to piece together chemical environments and physical processes that operated in our early solar system producing the planets and bodies that exist today. This is a Herculean task as much of the evidence lacks context or reflects a more recent, alteration or deformation history. Chondrites have bulk chemistries similar to that of the sun and preserve the history of the protoplanetary disk (i.e. gas and dust distributed in a disk-like fashion around a proto-sun prior to planet formation) and their parent body within their components. Similar to other valuable meteorite groups, the subsets of chondrites with highest scientific value are only available for research in small quantities. It is, therefore, important to maintain a delicate balance between sample preservation and contributing to the scientific knowledgebase from collection and curation through analysis. A combination of non-destructive techniques through the entire sequence from sample selection, preparation, and analysis maximizes scientific return while minimizing material loss.
So what exactly can chondrites tell us? To answer this, we first have to consider the variety of components that make up chondrites (Fig. 2). These components are categorized broadly as: calcium- and aluminum-rich inclusions (CAI), amoeboid olivine aggregates (AOA), chondrules, metal and sulfide nodules, and matrix. CAIs are highly refractory containing the greatest abundance of elements (i.e. Ca, Al, Ti) that condense from a vapor at high temperature, and minerals (e.g. corundum, hibonite, spinel, melilite) formed at high temperatures in the protoplanetary disk. CAIs exhibit a range of textures from primitive aggregates of tiny mineral grains to completely melted and recrystallized. AOAs typically have a core of highly refractory, CAI-like material but are then surrounded by olivine, a Mg-Si mineral that condenses at lower temperatures than the minerals in CAIs. As their name indicates, their texture is fragmented and clustered, with many of the olivine-rimmed refractory clumps arranged together at differing scales. Chondrules are diverse in composition but contain mainly Mg-Si minerals with varying Fe included to a varying degree. Many chondrules appear to have been completely melted prior to accretion while some may reflect a less melted, more agglomerated formation. Metal, generally Fe-Ni alloy, and sulfides can be common or rare depending on the conditions of chondrite formation. Matrix is the fine-grained material that holds all the chondrite components together. The percentage varies between types of chondrites and it is the most susceptible component, after metal and sulfides, to the effects of terrestrial alteration.
Different components and aspects of each component yield diverse information pertaining to characteristics of the early solar system and processes on parent bodies. Primitive, unmelted, CAI material holds the highest temperature record within its chemistry taking us back to a high-temperature protoplanetary disk (e.g. Ebel and Grossman, 2000; Grossman, 2010). Isotopic compositions can reveal the ages of components and define chemical reservoirs (e.g. Krot et al., 2005; Connelly et al., 2012; Holst et al., 2013). Composition, crystallization characteristics, and other features define the melting histories of components’ precursors including the temperature, duration, and extent of heating and potential formation processes (e.g. Jones and Rubie, 1991; Ebel et al., 2008; Krot and Bizzarro, 2009; Desch et al., 2010; Asphaug et al., 2011; Hubbard et al., 2012; Sanders and Scott, 2012; Johnson et al., 2015). Metal and iron content of certain minerals reflect how oxidizing or reducing conditions were and whether this condition varied in space or time (e.g. Connolly et al., 2001; Beck et al., 2012; Schrader et al., 2013). Size and abundance distributions of components among different chondrite types distinguish unique from shared histories among chondrite types (e.g. Cuzzi et al., 2001; Hezel and Palme, 2010; Friedrich et al., 2014). These are just a few examples of critical datasets and their potential implications. All in, chondritic components’, chemistry, proportions, textures, etc. provide constraints for the protoplanetary disk that astrophysicists try to model and for the pre-differentiation parent body processes in the early solar system.
Chondrites clearly contain a wealth of information that provides insight into the conditions of the protoplanetary disk and parent bodies even if only small percentages are recovered. A majority of meteorites studied today are collected through organized efforts, such as the Antarctic Search for Meteorites, which focus on sites in hot and cold deserts where meteorites are both preserved longer and can be concentrated. Terrestrial weathering essentially removes value from a sample as it alters much of the chemical and mineralogical information to reflect recent Earth surface rather than early solar system or chondrite parent body conditions. Falls are the most preferred specimens but are rare (Fig. 1), do not encompass all types of meteorites, and still suffer from terrestrial weather effects. To the planetary science research group at the American Museum of Natural History (AMNH) is guided by the thought that every meteorite sample should be handled and curated in a way that extracts as much information as possible about every aspect of the meteorite while preserving the sample for future use (Fig. 3), especially those samples that contain rare, valuable data about the early solar system.
At the AMNH, the analysis protocol for recent work begins with a trip to the in-house CT scanner (GE VtomeX-S x-ray computed tomography scanner) in the Microscopy and Imaging Facility. This instrument utilizes high-powered x-rays to produce data that is reconstructed into a 3-dimensional (3D) density map of the sample. Obtainable resolution, measured as the edge length of each cubic volume element, or ‘voxel’, depends on sample size, or distance from source, and size of focal spot; i.e. the best resolution for a sample 5x5x20 mm is ~4 micron/voxel on the scanner at AMNH (Fig. 3A and B). Resolution limits the types of analyses that can be conducted. Lower resolution allows virtual isolation (segmentation) and quantification of materials with significantly different densities (i.e. metals vs. silicates or chondrules vs. matrix) while higher resolution studies can differentiate different silicate and oxide minerals (e.g. Ebel et al., 2008; Friedrich and Rivers, 2013; Russell and Howard, 2013; Tsuchiyama et al., 2013). The 3D visualization permits analyses done in 2D to be placed into context (i.e. whether the mineral is in the core or rim of the chondrule) which could greatly affect interpretations. Component relationships and abundances can also be directly calculated from the CT data (e.g. Friedrich and Rivers, 2013; Russell and Howard, 2013; Goldman et al., 2014). While this technique can guide sample preparation, 2D analyses of surfaces are still required to address a majority of the component-based protoplanetary disk and parent body processes conundrums.
During sample preparation, cutting is the step that results in the most unrecoverable sample loss. Typical diamond embedded rock-cutting blades lose a >100 micron thick slice of material. Use of a 20, 30 or 50 micron tungsten (W) wire saw (Princeton Instruments) minimizes the thickness of material lost. This effectively minimizes sample loss and maximizes the number of surfaces that can be analyzed within a given piece of meteorite, a method called ‘serial sectioning’ (Fig. 3C; ps1B and ps2A are cut surfaces). This technique permits >100 micron diameter components to be exposed on two mirrored cut surfaces while larger components can be sectioned in more than two adjacent sets of surfaces (e.g. Ebel et al., 2008). The wire saw also produces a smooth surface requiring minimal grinding when the sample is polished for analysis.
Polishing is necessary to reduce surface topography which negatively affects most analysis techniques. Some techniques, such as electron microprobe (EMP) analysis, require a polish finished with 1 or 0.25 micron diamond solutions, while others, such as electron backscatter diffraction (EBSD), require extremely good polishes adding a chemical etching component with the use of colloidal silica. Diamond is a preferred polishing compound because it does not contaminate the sample with aluminum (Al) or silicon (Si) both which are of interest for components in chondrites. Alcohol or mineral spirits are preferred over water for polishing and rinsing because water may cause oxidation, reactions, or dissolution of some minerals. Successfully prepared samples can be coated with a thin layer of carbon to make them conductive, a necessity for use in most electron beam instruments.
The Cameca SX100 EMP at AMNH uses two types of spectrometers: wavelength dispersive and energy dispersive, to generate elemental concentration data for individual points or regions. Pixel-by-pixel element intensity maps (Fig. 3D) can be combined into red-green-blue (RGB) composites allowing differentiation between types of inclusions and minerals in meteorites over large, region maps (>1 micron/pixel) or individual inclusions (1 micron/pixel). Figure 2 illustrates zoom in of different components and figure 3E shows a component of interest outlined in white. Element intensities measured by the EMP are converted to oxide weight percent (wt%) via calibration against standards analyzed with the same instrument settings as the samples. A variety of software, either customized or packaged, can be used to evaluate each inclusion pixel-by-pixel using element intensity maps and combinations of ratios and cation formulas. A phase map is produced with each pixel assigned a false color indicating mineralogy as determined by element intensities (Fig. 3F). Bulk chemistry, mineralogy, modal abundance, texture, and area are quantifiable from either region or individual inclusion maps (Fig. 3G). The choice of analysis software will affect the time required for sample preparation, calibration, data acquisition, and image analysis and this choice is made based on the scale and focus of the study.
Up to this stage of analysis the techniques (CT, wire saw, polishing, EMP) are minimally destructive to the valuable samples. The data are used to evaluate and compare chondrite component characteristics including chemical composition, mineralogy, and textures. So, with minimal sample loss many scientific questions (major element chemical environments, abundances of components in chondrites, the mineralogy of chondrite components etc.) regarding the protoplanetary disk and parent body processes can begin to be addressed. Our group uses this protocol to build databases that provide contextual and quantifiable information about the early solar system that is accessible for reevaluation in the future. This preserves maximum data for the limited primitive, pristine chondritic samples that have been collected and catalogued.
This database serves as a resource for directing further analyses which can be more destructive or cost prohibitive (Fig. 3H). Electron backscattered diffraction (EBSD) provides crystal orientation information which is used to understand crystallization and deformation of mineral grains. Figure 4 depicts preliminary EBSD data that highlights twinning in metal found in a chondrule which will provide formation constraints (e.g. Crapster-Pregont et al., 2015). Secondary ion mass spectrometry (SIMS) is minimally destructive but may require travel and analysis costs as not all institutions maintain these instruments. Inductively coupled mass spectrometry (ICP-MS) requires either dissolving the sample into solution or blasting the point of interest with a laser while both can be done with minimal sample loss, this method may also require extra cost. Both SIMS and ICP-MS yield information about trace element abundances and even isotopic information yielding constraints on reservoirs and ages (e.g. Stracke et al., 2012; McCubbin et al., 2014) for SIMS and ICP-MS respectively). Focused ion beam liftout for transmission electron microscopy (FIB- TEM) can be used for extremely high-resolution chemical and orientation analysis of relationships within and among minerals within a chondrite component (e.g. Stroud et al., 2002; Stroud et al., 2003). EBSD, SIMS, ICP-MS, and FIB-TEM are just a few techniques implemented by planetary scientists to obtain detailed data from chondrites to continue addressing questions about the early solar system. However, unlike the protocol described above, each of these techniques requires sample consumption to produce data. While valuable sample is lost, the initial context and basic information from the chondrite is preserved in datasets from the minimally destructive analysis techniques.
Even though fewer meteorite samples exist in a catalogued database than are predicted to fall in a year, it is possible to optimize the analysis process with respect to the value of the chondrite and the information it contains. When combined these techniques (Fig. 3) reduce the amount of material lost and maximize the information obtained from a single meteorite sample. The larger set of data preserves contextual and quantifiable data for each CAI, AOA, chondrule, metal nodule, and matrix while guiding future, destructive analysis. By using a series of instruments, visualizations, and software protocols it is possible to begin to better understand the complexity of the protoplanetary disk, and planet formation processes preserved in meteorites with maximum conservation of these precious samples.
Acknowledgments: The Brian Mason Travel Award is sponsored by the International Meteorite Collectors Association for the 2015 78th Annual Meteoritical Society Meeting. Research is supported by the National Science Foundation Graduate Research Fellowship Program grant DGE-11-44155 and NASA Cosmochemistry grant NNX10AI42G. Fig. 1: Percentage bar representations demonstrate the rarity of and necessity to fully analyze chondrites and their components. Percentages for predicted annual impacts of meteorites (Bland, 2005) are far greater than those collected, classified, and catalogued (top bar: 2014 data from the Meteoritical Society Bulletin Database). When all meteorites in the Database are considered the remaining percentage bar comparison show: iron, achondrite, or chondrite; whether a find or the much less common observed fall; exhibiting parent body alteration or pristine; and whether the component is composed of minerals predicted to condense at highest temperature (refractory) in the protoplanetary disk. All percentages are based on number not mass.
Fig. 2: Backscattered electron image (BSE) of Moss (CO3.6) AMNH #5185 with examples of different components boxed with corresponding outset false color, 3-element red-green-blue composite images. The 3-element combination Mg-Ca-Al clearly distinguishes calcium- and aluminum-rich inclusions (CAI; primarily blue and green), chondrules (primarily red), and amoeboid olivine aggregates (AOA; blue and green core with red surrounding) from each other. While metal appears black in the Mg-Ca-Al images the combination of Fe-Ni-S permits chemical variation observation for the metal nodules and metal in the AOA. Matrix is a darker red color highlighted in the white box within the corresponding image of a different component.
Fig. 3: Preparation and analysis protocol for minimizing sample loss and maximizing data. (A) Photo of Moss (CO3.6) AMNH #5185; (B) single CT slice, high density is whitest; (C) post-wire saw sections; (D) EMP element intensity maps for aluminum (Al), calcium (Ca) and magnesium (Mg) with inclusion outlined; (E) RGB composite, note ease of distinguishing inclusion; (F) false color mineral map output: purple-spinel, red-olivine (olv), green-clinopyroxene (cpx); (G) quantitative data produced; (H) further destructive techniques possible using a high level of prior contextual knowledge (A-G).
Fig. 4: Electron backscatter diffraction (EBSD) generated false color, reverse pole figures maps for a whole metal nodule (a; 2 μm/pixel) and higher resolution portion of a different nodule (b; 0.5 μm/pixel) in the second metal layer in the Acfer 139 layered chondrule. Color represents the orientation of the metal at each pixel described by the mixing chart in the center of the figure where each apex is a different crystal axis. Small wire-frame cubes highlight the orientation of various regions. Lamellar-like features are twinning not artifacts of the polishing process. Image unmodified from (Crapster-Pregont et al., 2015) with permission.
References:
Asphaug E., Jutzi M. and Movshovitz N. (2011) Earth and Planetary Science Letters. Earth and Planetary Science Letters 308, 369–379.
Beck P., De Andrade V., Orthous-Daunay F. R., Veronesi G., Cotte M., Quirico E. and Schmitt B. (2012) The redox state of iron in the matrix of CI, CM and metamorphosed CM chondrites by XANES spectroscopy. Geochimica et Cosmochimica Acta 99, 305–316.
Bland P. A. (2005) The impact rate on Earth. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, 2793–2810.
Bland P. A., Berry F. J., Smith T. B., Skinner S. J. and Pillinger C. T. (1996a) The flux of meteorites to the Earth and weathering in hot desert ordinary chondrite finds. Geochimica et Cosmochimica Acta 60, 2053–2059.
Bland P. A., Smith T. B., Jull A. J. T., Berry F. J., Bevan A., Cloudt S. and Pillinger C. T. (1996b) The flux of meteorites to the Earth over the last 50 000 years. Monthly Notices of the Royal Astronomical Society 283, 551–565.
Connelly J. N., Bizzarro M., Krot A. N. and Nordlund Å. (2012) The absolute chronology and thermal processing of solids in the solar protoplanetary disk. Science 338, 651–655.
Connolly H. C. Jr, Huss G. R. and Wasserburg G. J. (2001) On the formation of Fe-Ni metal in Renazzo- like carbonaceous chondrites. Geochimica et Cosmochimica Acta 65, 4567–4588.
Crapster-Pregont E. J., Towbin W. H. and Ebel D. S. (2015) Metal-Centric Perspective of a Layered Chondrule in the CR Chondrite Acfer 139: Insights from Electron Backscattered Diffraction. Lunar and Planetary Science Conference Proceedings. Abstract #1561.
Cuzzi J. N., Hogan R. C., Paque J. M. and Dobrovolskis A. R. (2001) Size-selective concentration of chondrules and other small particles in protoplanetary nebula turbulence. ApJ 546, 496–508.
Desch S. J., Morris M. A., Connolly H. C. and Boss A. P. (2010) A Critical Examination of the X-Wind Model for Chondrule and Calcium-Rich, Aluminum-Rich Inclusion Formation and Radionuclide Production. ApJ 725, 692–711.
Ebel D. S. and Grossman L. (2000) Condensation in dust-enriched systems. Geochimica et Cosmochimica Acta 64, 339–366.
Ebel D. S., Weisberg M. K., Hertz J. and Campbell A. J. (2008) Shape, metal abundance, chemistry, and origin of chondrules in the Renazzo (CR) chondrite. Meteoritics and Planetary Science 43, 1725–1740.
Friedrich J. M. and Rivers M. L. (2013) Three-dimensional imaging of ordinary chondrite microporosity at 2.6 micron resolution. Geochimica et Cosmochimica Acta 116, 63–70.
Friedrich J. M., Weisberg M. K., Ebel D. S., Biltz A. E., Corbett B. M., Iotzov I. V., Khan W. S. and Wolman M. D. (2014) Chondrule size and related physical properties: A compilation and evaluation of current data across all meteorite groups. Chemie der Erde – Geochemistry, 1–25.
Goldman R. T., Crapster-Pregont E. J., and Ebel D. S. (2014) Comparison of Chondrule and CAI Size Measured by Electron Microprobe (2D) and Computed Tomography (3D). Lunar and Planetary Science Conference Proceedings. Abstract #2263.
Grossman L. (2010) Vapor-condensed phase processes in the early solar system. Meteoritics and Planetary Science 45, 7–20.
Halliday I., Blackwell A. T. and Griffin A. A. (1989) The flux of meteorites on the Earth’s surface. Meteoritics 24, 173–178.
Hezel D. C. and Palme H. (2010) The chemical relationship between chondrules and matrix and the chondrule matrix complementarity. Earth and Planetary Science Letters 294, 85–93. Holst J. C., Olsen M. B., Paton C., Nagashima K., Schiller M., Wielandt D., Larsen K. K., Connelly J. N., Jorgensen J. K., Krot A. N., Nordlund Å. and Bizzarro M. (2013) 182Hf–182W age dating of a 26Al-poor inclusion and implications for the origin of short-lived radioisotopes in the early Solar System. In Proceedings of the National Academy of Sciences of the United States of America. pp. 8819–8823.
Hubbard A., McNally C. P. and Mac Low M.-M. (2012) Short Circuits in Thermally Ionized Plasmas: A Mechanism for Intermittent Heating of Protoplanetary Disks. ApJ 761, 58.
Johnson B. C., Minton D. A., Melosh H. J. and Zuber M. T. (2015) Impact jetting as the origin of chondrules. Nature 517, 339–341.
Jones R. H. and Rubie D. C. (1991) Thermal histories of CO3 chondrites: application of olivine diffusion modelling to parent body metamorphism. Earth and Planetary Science Letters 106, 73–86.
Krot A. N. and Bizzarro M. (2009) Chronology of meteorites and the early solar system. Geochimica et Cosmochimica Acta 73, 4919–4921.
Krot A. N., Yurimoto H., Hutcheon I. D. and MacPherson G. J. (2005) Chronology of the early Solar System from chondrule-bearing calcium-aluminium-rich inclusions. Nature 434, 998–1001.
McCubbin F. M., Shearer C. K., Burger P. V., Hauri E. H., Wang J., Elardo S. M. and Papike J. J. (2014) Volatile abundances of coexisting merrillite and apatite in the martian meteorite Shergotty: Implications for merrillite in hydrous magmas. American Mineralogist 99, 1347–1354.
Russell S. S. and Howard L. (2013) The texture of a fine-grained calcium-aluminium-rich inclusion (CAI) in three dimensions and implications for early solar system condensation. Geochimica et Cosmochimica Acta 116, 52–62.
Sanders I. S. and Scott E. R. D. (2012) The origin of chondrules and chondrites: Debris from low-velocity impacts between molten planetesimals? Meteoritics and Planetary Science 47, 2170–2192.
Schrader D. L., Connolly H. C. Jr, Lauretta D. S., Nagashima K., Huss G. R., Davidson J. and Domanik K. J. (2013) The formation and alteration of the Renazzo-like carbonaceous chondrites II: Linking O-isotope composition and oxidation stateof chondrule olivine. Geochimica et Cosmochimica Acta 101, 302–327.
Stracke A., Palme H., Gellissen M., Münker C., Kleine T., Birbaum K., Günther D., Bourdon B. and Zipfel J. (2012) Refractory element fractionation in the Allende meteorite: Implications for solar nebula condensation and thechondritic composition of planetary bodies. Geochimica et Cosmochimica Acta 85, 114–141.
Stroud R. M., Long J. W., Swider-Lyons K. E. and Rolison D. R. (2002) Transmission electron microscopy studies of the nanoscale structure and chemistry of Pt50Ru50 electrocatalysts. Microscopy and Microanalysis 8, 50–57.
Stroud R. M., Nittler L. R., Alexander C. M., Bernatowicz T. J. and Messenger S. R. (2003) Transmission electron microscopy of non-etched presolar silicon carbide. Lunar and Planetary Science Conference XXXIV. Abstract #1755.
Tsuchiyama A., Nakano T., Uesugi K., Uesugi M., Takeuchi A., Suzuki Y., Noguchi R., Matsumoto T., Matsuno J., Nagano T., Imai Y., Nakamura T., Ogami T., Noguchi T., Abe M., Yada T. and Fujimura A. (2013) Analytical dual-energy microtomography: A new method for obtaining three-dimensional mineral phase images and its application to Hayabusa samples. Geochimica et Cosmochimica Acta 116, 5–16. Meteorite Times Magazine
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Once a few decades ago this opening was a framed window in the wall of H. H. Nininger's Home and Museum building. From this window he must have many times pondered the mysteries of Meteor Crater seen in the distance.
Photo by © 2010 James Tobin