Lost Identity

I received the image below in my email today.  The sender had purchased a collection of 700 “minerals”, none of which had any labels or other identifying information.  He wanted to have testing done to determine this iron meteorite’s identity.  Unfortunately, all testing will do is determine which chemical group (for example:  IAB-MG) this meteorite belongs to.  Canyon Diablo, Campo del Cielo, and Odessa (all once commonly sold as large hand samples) are all IAB-MG irons.  Chemical tests will not distinguish these from each other.

Unidentified iron meteorite

Unidentified iron meteorite

So this meteorite joins a very large group of meteorites who have lost their identity.  This makes them almost useless to researchers, and also makes them less valuable to collectors.  I see this much too often.  Sometimes it is because a collector didn’t bother to label things, but not always.

A few years ago, we got a call from a brother and sister.  Their father had died abruptly (and way too young – mid 50s).  He had an extensive (and carefully documented) collection of meteorites.  Unfortunately, the brother and sister had pulled everything out and separated the samples from their boxes and labels.  Now they needed help trying to match things back up.  We were able to match most, but not all of the samples to the inventory.  The identified samples were put on ebay for a quick sale, and the unidentified samples were given to the lab (as opposed to being tossed).  I am sure the collector would have been horrified to see what happened to his meteorites.

So, if you are a meteorite collector and you care about your collection, what should you do?  First, think about what would happen if you died abruptly (car accident, drive-by shooting, etc.).  What have you done with your collection?  Hopefully, you have everything accompanied by a label.  But, as labels can be lost, you should also have an inventory with images of each sample accompanied by all the information you have about that sample (where did you obtain it/from which dealer did you obtain it, when did you obtain it, how much did you pay for it, weight of sample, approx size of sample, etc.).

Now, who gets your collection when you’re gone?  You’ve left it to you nephew.  Does he want the collection?  Or does he want the money he could get from selling your collection? Do you care if he sells your collection?  If not, then no problem.  If you want to keep your collection intact, you should think about leaving it to a meteorite repository (such as the Cascadia Meteorite Lab).  You can find a list of official meteorite repositories on the Meteoritical Bulletin Database website (look for the green check mark next to the name–it means the repository has been approved by the Meteoritical Society).  Contact the repository.  Check them out to see if you’re happy with them.  Give them a copy of your inventory and a copy of the relevant page(s) of your will.  Let your lawyer and your heirs know that you intend to leave your samples to the repository.

Please, think about it.  We don’t need more meteorites that lack identities.

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It’s a dark rock

Everyone has been super busy at the lab, and posts to our blog are the first thing to “slide”. But we continue to answer e-mails from the public.  We’re receiving around 4 or 5 email requests per day, which adds up to well over a thousand each year.  In the past couple of days, I’ve gotten emails which have started me thinking about perspective and expectations.  One email sent images along with a suggestion that I am “intolerant” or somehow close-minded about samples. A second email asked me for information about free/no-cost testing for their samples.  A third email enclosed numerous blurry photos of a dark object against a white background (which is all too common).  I post one of those photos below.

Is it a meteorite?

Is it a meteorite?

I’ve realized that, for the most part, the people sending in these images don’t really understand what we do in our lab. I have a fantasy where I think these people envision large numbers of “scientists” in white coats surrounded by analytical equipment sorting through boxes and boxes of rocks.  All of the equipment can be used for free and quickly and effortlessly analyzes each rock.  Reality is so different.

Our lab is a small university research lab (which is not that atypical of meteorite labs at universities).  We have two faculty who can use analytical equipment to analyze samples (Alex Ruzicka and Melinda Hutson).  We are paid salaries to be faculty, by which I mean a) teach classes (several per term), b) work with undergraduate and graduate students on research projects, c) obtain grant funding for specific research projects, d) do the work required by the grant funded project, e) serve on university committees, etc.  There are no funds to actually run the meteorite lab, analyze any samples that are not part of a grant-funded project, or curate the samples in the collection.  The funding that runs the Cascadia Meteorite Lab comes entirely from public donations.  We have been fortunate to have a steady stream of donations.  But we do have to be choosy about where we spend money.  None of the analytical equipment is free.  If we analyze a stone, it costs our lab money. The other thing to note is that we are fully employed doing the jobs for which we receive salaries.  Answering emails, examining photos, and rarely analyzing a rock are things we volunteer our very limited time to do.

So, given the constraints of limited time and limited funds, what do we do about 1000-2000 requests from the public regarding samples?  Well, we spend what time we can looking at images and writing e-mails (which takes more time than we’d like).  Images come in three categories:  1) yes it is an obvious meteorite — this doesn’t happen often; 2) no, it is definitely not a meteorite–I can tell this without knowing the actual identity of the sample–please don’t email me asking what it is; and 3) I can’t tell from your photo–which unfortunately is most of the time.  If an image is in category 2 or 3, I don’t really have the time to do anything else with it.  If the sample is an obvious meteorite, I may still not have the time or funds to do anything else with it, but I will try to point people to someone who might be able to help them.

I literally can afford to analyze only about two dozen new meteorites per year if they are not part of a grant funded project.  Classifying a meteorite involves having a thin section made (either time or money), examining the thin section with an optical microscope (time), obtaining mineral chemical data using either an electron microprobe or a scanning electron microscope (time and money), making sense of this data (reducing the data – time), writing up the classification and submitting it (yet more time).  And this assumes a relatively easy stony meteorite (like a high type chondrite). Complicated samples require additional information (such as oxygen isotopes– which takes time and money to obtain).

We get students involved in classification.  This is great for the students.  They learn a lot.  It is slower than actually doing the work ourselves.

So, it isn’t that I’m not open to possibilities, or that I don’t want to see every possible meteorite out there.  I’m constrained by time and funding to looking at a very few samples each year.  So, I’m going to be very very choosy and pick very very obvious meteorites.

The public, bless ’em

The Cascadia Meteorite Laboratory (CML) is comprised of Alex Ruzicka, Melinda Hutson, Dick Pugh, and an ever varying group of students.  Between the three of us (Alex, Melinda, and Dick), we get e-mails, letters, and phone calls from 5-12 people per day asking if they’ve found a meteorite.  Yup, per day. Some of those contacts include repeats from people who want clarification or want to argue, or just want to comment (often rudely) on our opinions.  We also hear from a lot of people that we are one of the few places that actually respond to public inquiries.  That is because the public (bless ’em) include a small number of people who fall under the category of “pest” or “incredibly rude”.  And despite their numbers being a small percentage of the contacts, there are enough that most scientists reach a point where they simply don’t want to deal with these people anymore.

As an example:  Yesterday, I opened my e-mail to find 9 messages from the public.  I had a very short window of time before a meeting to answer all of these.  One of the nine messages said:

“Found this hiking in the woods with my family. Delaware county, PA suburbs of Philadelphia.”

In addition to this one sentence (which is a statement, and which doesn’t actually ask my opinion on anything), there were four photos (one is below – it was originally 1.5 Mbytes).

CAM00043My response was:

“I am sorry to disappoint you, but your sample is very clearly not a meteorite. It is some sort of fine-grained terrestrial rock (I can think of several candidates). But the texture is NOT meteoritic. I’m enclosing one of our lab’s promotional flyers, which has information about identifying meteorites.”

Unlike the message to me, I included a salutation “Dear …” and a signature.

This morning, I received a response:

“How completely dismissive. No other questions about it, huh? About the layer of rust covering it? Or the shiny metallic specs all through out the window for the sample i was going to send you? Or how it passed the “streak test”? And also its weakly magnetic. How scientificly thorough of you to gather all those conclusions from those highly detailed photos.”

My response to such scintillating sarcasm is to not respond, blacklist the email address, and use this as an example of how not to approach a meteoriticist.  At least this one didn’t contain any obscenties or personal insults.

For those who are interested in asking about a possible meteorite, I have some suggestions:

1) Realize that the meteorite specialist is familiar with real meteorites and that they’ve seen thousands and thousands of photographs of things that are not meteorites.  Sometimes it is not clear from a photo whether or not the sample is a meteorite, and sometimes it is (in this case, it was obvious).

2) Be polite.  Realize that if you decide to get snarky, you are contributing to the eventual burnout of the meteorite specialist for dealing with the public.  Everyone else will not appreciate having fewer and fewer specialists available.

3) Try to actually write out a short letter.  If you can’t write “Dear Dr. …”, then how about “Hello”.  Then think about asking for an opinion.  Then sign your name.  I’ve gotten e-mails with nothing but a photo (no text at all) and an email address along the lines of xyz123@company.com.  I find myself responding “Dear xyz123@company.com:  I’m assuming you are asking me to identify your rock.  It is not a meteorite.  Sincerely, Me.”

Ordinary Chondrite Classification: Shock

There was a discussion about shock classification and a type 3.00 chondrite on the meteorite list recently.  It was assumed by some that a type 3.00 chondrite could not have experienced shock.  I went back to Stoffler, Keil and Scott 1991 to look at the pressures and temperatures for the different shock stages.  Turns out there is very little heating (approx. 10-20 degrees C) for low shock stages (such as S2), certainly not enough to “metamorphose” a chondrite.  But re-reading this paper got me thinking about how one determines the shock stage of an ordinary chondrite.

Stoffler, et al. 1991 is the paper that explains how to determine shock stage in an ordinary chondrite. Classification information is summarized   in Table 1 of their paper.  A slightly different version of their table is found in a nice article on shock effects in ordinary chondrites published by PSRD (http://www.psrd.hawaii.edu/April04/asteroidHeating.html ).  Shock stages are based primarily on deformation of olivine grains.  The PSRD article has some good illustrations of “shocked” olivine grains.

Deformed (showing mosaic extinction) olivine in the Morrow County (CML 0497) chondrite (L6 S5 W1).

Deformed (showing mosaic extinction) olivine in the Morrow County (CML 0497) chondrite (L6 S5 W1).

If one actually reads through Stoffler, et al. 1991, one sees that shock stage should be determined by examining “ten to twenty of the largest, randomly distributed olivine single crystals with high interference colors, at least 50-100 microns in size “, viewed in cross-polarized light, and preferably a 20x objective.  Also, Stoffler, et al. 1991 “recommend to choose the highest shock stage shown by any significant fraction of grains (at least 25%) to establish the shock level of a chondrite.” They also note that “When we assign a shock stage to such a breccia, it is our estimate of the equilibration peak shock pressure experienced by the whole rock.”

This is a very specific description of what to do, and I suspect that many classifiers don’t do this.  The reason for using the largest grains is to eliminate apparent deformation due to overlapping grains (one on top of another).  It is expected that there will be some variability in the appearance of the grains, as shock effects will never be 100% uniform through a multi-mineral/crystal rock. This is why one is supposed to choose the highest shock stage shown by at least 25% of the olivine grains.  Whether the chondrite is a breccia or not, the classifier is supposed to come up with only one number for the shock stage (e.g., S4, not S3-5).

It is not as simple as it sounds.  Breccias in particular are difficult.  It is not at all clear that one can figure out the peak pressure experienced by the whole chondrite from a single thin section of a breccia (a meteorite made up of multiple clasts, each of which has a different thermal and shock history).  We prefer to give the range seen by the lithologies in the particular section we’ve used for classification. Non-breccias are not necessarily simple either.  Our lab has two thin sections of Tenham.  One has an S6 shock vein containing high pressure minerals, such as ringwoodite.  The chondritic material outside of the vein is of shock stage S5.  But a second section, lacking the S6 shock vein, has olivine consistent with a shock stage of S4.  It is clear that the olivine experienced higher shock pressures/temperatures near the vein.

Two thin sections of the Tenham chondrite (CML 0337).

Two thin sections of the Tenham chondrite (CML 0337).

Finally, Alan Rubin has proposed that many chondrites, including Portales Valley have experienced “post-shock annealing”, which has removed deformation from olivine grains, causing the optical shock classification to be somewhat-to-much lower than the actual peak shock experienced by the meteorite.  Preliminary work by Hutson et. al. (2007) using transmission electron microscopy (http://www.lpi.usra.edu/meetings/metsoc2007/pdf/5072.pdf ), suggests that this is indeed the case (although we are not in agreement with Rubin as to the extent of annealing).

 

 

Imaging and information

I recently got an e-mail asking whether or not a thin section needed to be prepared in order for a chondrite to be classified.  The answer according to some scientists doing classification is “no”, while others feel “yes” is the correct answer.  Why the disagreement?  It depends on the point of view of the classifier.  If your end goal is to quickly determine whether or not a chondrite is equilibrated (means all of the grains of one type of mineral have the same chemistry) or not, and to obtain chemical data on the mineral grains, then using a Scanning Electron Microscope (SEM) on a polished sample (bulk or in an epoxy plug) will suffice.

On the other hand, if you are one of those people who wants to do a thorough and complete job (including shock stage), with an eye open for oddities that potentially lead to research projects, then you need a thin section.

Backscattered Electron Image of a barred olivine chondrule in an R chondrite.

Backscattered Electron Image of a barred olivine chondrule in an R chondrite.

Above is an image taken with the SEM of a barred olivine chondrule.  As the chondrite is equilibrated, all of the olivine grains are the same color and it is hard to distinguish individual grains.  Below is an image taken with an optical microscope of the same chondrule (with polarizing filters).  It is much clearer that the chondrule is surrounded by clusters of very small olivine grains.  The variation in color (from blue to purple) indicates that part of the chondrule is “mis-oriented” relative to the rest of the chondrule, due to shock.  If the sample were unshocked, the chondrule should be a uniform color.

Cross-polarized view of a barred olivine chondrule in an R chondrite.

Cross-polarized view of a barred olivine chondrule in an R chondrite.

On the other hand, optical microscopy misses some of the details observed with an SEM. Below is a backscattered electron (BSE) image of a chondrite which contains “relict” olivine grains (chemically inhomogenous grains with a magnesian cores (dark areas), surrounded by equilibrated (uniformly colored) olivine grains)

Relict olivine grains in a chondrite.

Relict olivine grains in a chondrite.

What it comes down to is how much time you want to spend on classification.  And that depends in part on how interesting you think the sample is.  I always spend more time than I probably should on a classification, but that has led to a number of research projects over the years.

More ruminations on thin sections

I’ve been looking at a lot of poorly polished thin sections lately (see previous post on polish).  But polish isn’t the only thing to worry about when making thin sections.

Below are images [used with permission of Dr. Allen Glazner at UNC] of two minerals that are very common in ordinary chondrites (orthopyroxene/hypersthene and olivine).  In fact, L-chondrites used to be called olivine-hypersthene chondrites.  The UNC website shows features students can use to identify the minerals.  These include “interference colors” (mineral color when viewed with cross-polarized light).  Anyone who has taken an optical mineralogy course will be familiar with one of several charts that show the interference colors of various minerals.  But these colors depend on the thickness of the sample in thin section.  The information below is for a standard sample thickness of 30 microns.  Low-calcium orthopyroxenes are typically yellow, brown colors, while olvines are vibrant green, pink, blue.  For rocks which have not experienced much shock, orthopyroxenes will generally have fractures in two directions at approximately right angles (cleavage planes), whereas olivine will have very few fractures.

images o forthopyroxe and olivine in cross-polarized light

images of orthopyroxene and olivine in cross-polarized light

But meteorite parent bodies have experienced impact events that create shock effects in mineral grains.  Olvine that is shocked may have one or more sets of relatively straight (planar) fractures.  In the image (in cross-polarized light) below, olivine bars in the Jungo 001 L6 chondrite (shock stage S4) have brightly colored interference colors, but are also full of fractures.

olivine bars in Jungo 001 showing evidence for shock deformation

olivine bars in Jungo 001 showing evidence for shock deformation

Below is an image (in cross-polarized light) of the Buck Mountains 005 L6 chondrite (also shock stage S4).  Some bright colors are visible indicative of olivine, but much of the material shows the yellow, brown, white colors expected of orthopyroxene.  However, most of this is also olivine.  The thin section is slightly too thin, which moves all of the interference colors towards lower orders.  It turns out that for some reason, most of the pyroxene in this meteorite is in the form of clusters of small grains.  So almost every large grain is olivine, even though with the fractures and the lower-order interference colors, some grains look more like orthopyroxene.

Buck Mountains 005

Buck Mountains 005

For reasons beyond the scope of this post, it was necessary to prepare this particular thin section fairly quickly for electron microprobe analyses.  I did not have the chance to examine it with a scanning electron microscope first (as is my custom), nor did I have that much time to look at it with an optical microscope.  I took a very quick look and marked a few grains that I hoped would be orthopyroxene (I could tell I was seeing mostly olivine, but with an L6 chondrite there should be quite a bit of pyroxene as well).  In most cases, I guessed wrong, and analyzed olivine instead.

So a good thin section is not only one that is well polished, but one that has the correct thickness.  And obtaining that thickness is an art, as the final stages of polishing thin the sample down while producing a smoother surface.

Life of the Lab: Silicate inclusions in iron meteorites

Why do we choose the particular research areas that we study?  The answer is a mixture of random chance, serendipity, and following the funding.  What does that mean?  An initial idea can form as a result of a conversation, reading a journal article, observing something interesting in a meteorite that we are classifying, etc.  But to become a research project, that idea has to be fleshed out and somehow funded.  The publications from our lab represent a lot of examples of variations on this process.  One example is trying to understand how iron meteorites (which are very dense) could contain low-density silicate inclusions.  The two materials should rapidly unmix (like oil and water).  We’ve worked on this topic and published three refereed journal articles on the subject:

1) Ruzicka A. and M. Hutson (2010) Comparative petrology of silicates in the Udei Station (IAB) and Miles (IIE) iron meteorites: Implications for the origin of silicate-bearing irons. Geochim. Cosmochim. Acta 74, 394-433.

2) Ruzicka A. and M. Hutson (2006) Differentiation and evolution of the IVA meteorite parent body: Clues from pyroxene geochemistry in the Steinbach stony-iron. Meteorit. Planet. Sci. 41, 1959-1987.

3) Ruzicka A., M. Hutson and C. Floss (2006) Petrology of silicate inclusions in the Sombrerete ungrouped iron meteorite: Implications for the origins of IIE-type silicate-bearing irons. Meteorit. Planet. Sci. 41, 1797-1831.

The conclusions in all of these papers involve variations on a combination of collisions while the parent body is undergoing internal heating and/or differentiation.

But where did the idea for this research project come from?  None of us had previously worked on iron meteorites (or even metal in chondrites).  Many years ago, Alex Ruzicka, the lab’s director, visited the American Museum of Natural History, and wound up having a conversation with the late Marty Prinz about silicates in the Sombrerete ungrouped iron meteorite.  Alex became interested, applied for NASA grant funding, and … didn’t get it. 

So, Alex went back to Portland State University, and applied for “seed money” from the Faculty Develpment program, which (among other things) awards small grants to faculty to help them obtain a small amount of data in order to go after a larger grant.  Three years after the original grant proposal, Alex submitted a new grant proposal to NASA.  This one was funded.  The first meteorite we examined was Sombrerete, which turned out to be the key for understanding the other meteorites in the study. 

sil-irons

Above:  Top left are two images showing two sides of a small sample of Sombrerete – the metal is silver, the silicate inclusions are dark (the ruler is in millimeters); Top right:  A mosaic of reflected light images of Sombrerete inclusions set in metal; Bottom: Backscattered electrom (BSE) image of a phosphate-rich “arc” in one of the silicate inclusions.  The bright area in the extreme upper right of the BSE image is the host metal.