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Mysteries Solved at the Saw

It has been exciting several months. I have done a great amount of meteorite cutting for our business and a couple friends. I have been finding as I cut that what the friends thought they had was not always what I found at the saw. The most enjoyable of these fortunate mistakes was a batch of stones that were supposed to be carbonaceous chondrite and seemed to not be. I made several cuts into the first stone and it was weird material. I put a rare earth magnet on the stone and it slid off. There was no visible metal and from the reaction of the magnet, there was not any iron response from the mineral portion either. There were some chondrules and the stone was brecciated. I knew it was not carbonaceous but what I was thinking it might be required me to go to my office and look at the met bulletin and do some other research.

I have cut a few R chondrites over the years. It is usually one stone or maybe two but never very much and they have always been something already classified. To be honest my first-hand knowledge of R chondrite identification was a little lacking. I remember reading about them in books but had to check the characteristics I was seeing at the rock saw to confirm if my guess of R type chondrite was even possible. The no visible metal and low metal in the mineral portion were things I knew about R chondrites. When I found that almost 50 percent of R chondrites were breccias which was another important fact. I continued the research with looking at all the images I could find and several were quite similar to what was on the saw.

I messaged Jason Phillips who owned the stones and let him know what I was guessing. I did not want to cut more of the stone in the normal size and thickness slices if it was an R chondrite. It might make them too expensive at $25 per gram for people to afford and I would have to rework them smaller. He agreed and asked me to prepare a piece to send directly to a lab for classification. I smoothed up a slice just over 25 grams. It was nicely brecciated and would work well for classification. I put it in the mail with a letter explaining the circumstances of my discovery and what I guessed.

I packaged up the slices I had cut after finishing the lapping and polishing. I sent the material back to Jason and we waited to hear what the scientific world would say. We did not have to wait long. Within just several days the type specimen had gone through a preliminary examination and it was looking like an R3. This was pretty exciting news. I love being in on the ground floor of meteorite classification. It was going to take a while for thin section preparation and the rest of the research to be done to verify the initial R3 identification. Actually, about 6 weeks to just get the thin section made. Had I known it was that long a wait I could have made one and sent it along with the type specimen.

One learns to be patient when waiting for meteorites. It seems at every level meteorites require us to relax and wait. Some take a long time to cut successfully. They take their sweet time in arriving at Earth and they require patience and persistence to find in the field. But waiting for classification is waiting that is out of my control and I have more trouble with that when the specimen is something exciting. I got an occasional email as Jason checked with his scientist on the progress. Then the day came that we heard that the meteorite was approved and in the Meteorite Bulletin Database. I was so convinced by the time that I sent the type specimen off for classification that it was an R3 that Paul and I had bought a bunch of it for the business. I was at Paul’s home for a weekend of astrophotography when we got the news from Jason that the meteorite was officially approved. NWA 11721 was the newest R3 chondrite. I have to admit that I was also relieved a little that the purchase we had made without know for sure was going to be what I had guessed and not something of much less value.

About the same time that I was cutting the R3 chondrite I was cutting the end off another stone that was rather ordinary in appearance on the outside. But as it turned out it was “ordinary” in the same way Ordinary Chondrites are ordinary; fascinating and unique. It was special and very cool. It was densely packed with very visible chondrules that looked to be in great shape. I will warn you that as of this writing this meteorite is still in the process of being classified and is not official yet. But from the very start I was told it was likely an LL3. I am still waiting to see if that turns out to be true. I have a few meteorites at this point in my life but very few of them are striking type 3 chondrites with dense pristine chondrules. And my pieces of types like that are not big specimens. As soon as I saw the stone after the first cut I knew it needed to go off for classification. Within a few days I decided to see if I could buy the stone, which I did. I took two slices off the side of the mass. One was to keep as a beautiful addition to my Riker box collection the other was to become the type specimen and to make thin sections from. Of course I finished preparing the main mass also. I prepped the piece going off for classification. I sliced up the other portion so I had seven wafers of nice size for thin sections. I mounted them after lapping and polishing the glued side. The thin sections came out very nice. All were good but one was especially even and flat. As it turned out I made three of them thinner and four not quite as thin. I would later thin three of those down too. But unfortunately one would never get that final thinning. I posted some images of the meteorite on Facebook and got an email very quickly from Dr. Hutson at Cascadia Meteorite Laboratory that she thought it was a perfect candidate for some research that they are doing on clustered chondrules. I was thrilled to send them the type specimen and offered them that thin section which was especially nice to do the classification work from. She had asked me where I got my thin sections and I had told her I make them myself. They were looking for another source. I gave her a few names of companies we have used over the years. I said “If the thin section is not good enough for your use that is OK just keep it, maybe it will be good for the optical microscope work at least if not the microprobe work.”

I packaged up the type specimen and thin section and off they went. I heard in a few days that they were there and that the meteorite had plenty of chondrule clusters and might be fine for the research. That was really exciting for me. I have never had one of my discoveries used in a research project. Also, the thin section was good enough for them to work from. They would have to repolish it with colloidal silica for the microprobe but otherwise, it was OK. That was also exciting. I had not until recently felt my thin sections were close enough to 30 microns to be used in a laboratory setting but the ones I have made in the last year or so are really close. And the older ones I have reworked thinner most of them are also very close now.

The meteorite was immediately guessed from my Facebook photos to be a type LL3. The fact that the matrix of the meteorite was nearly all FeS was regarded as further evidence of it being an LL3. The chondrules are surrounded by the distinct bronze colored mineral and the space between chondrule when there is space is filled with it. There really is no fine grain stony matrix in the meteorite. It is just densely packed chondrules and a thin fill of FeS and a little nickel-iron metal.

It is that period of time now when I wait to hear back about the meteorite. I hope that it arrived at Cascadia Meteorite Lab in time to be useful in the research. I hope that my thin section was actually used for the work and that they did not have to have another made. I will feel a little bad if they did for I sent them nothing by way of a donation for the classification work this time since they had sought me out being interested themselves in the stone. I like working with them and they are friendly people I will make it up in the next submission if they went to extra trouble on the meteorite I am still calling the “Maybe LL3.”

I did not make any thin sections of the R3. We have slices of it for sale at our sales site and I will put a link in at the end. I think a thin section or two of it will happen in the future when that meteorite comes back to the saw again for more pieces to be made. Rummuruti type meteorites are not very common and type 3 R chondrites are quite scarce. In the Met Bulletin Database, less than 30 are listed as R3. Others are mixtures of petrological types and recorded in the database as R3-5 or R3-6 many are more specifically defined with a decimal such as R3.8 or R3.9. Sometimes that refined classification can make these stones extra cool. NWA 11721 is described as follows. “Breccia composed of angular clasts in a matrix of related debris. Clasts contain well-formed, separated unequilibrated chondrules (apparent diameter 310±200 µm, N = 15) set in a finer grained metal-free matrix. Accessory minerals are sodic plagioclase, troilite, Ti-chromite and chlorapatite.” It seems to be a true R3 which makes me happy as I love type 3 meteorites of all classifications.

I will refrain from using the Forrest Gump quote and just say that meteorites are mysterious. Their outside appearance is often deceiving. You may think that you have a certain thing only to be surprised after the first cut. It has happened to me many times that I expected a really weathered stone and found it was actually pretty fresh inside or anticipated from the outside another piece of something common in a batch of meteorites from one location only to find that it was not, for example, another NWA 869 but something different mixed into the batch. Provenance is absolutely important but it really only goes so far. And maintaining perfection in inventory control also absolutely necessary. Yet, more than one meteorite lands in a single location over thousands of years. After enough time in the same terrestrial environment, they may weather similarly. It requires attention at the saw to determine if the stone being cut matches all the characteristics of what is supposed to be getting cut. Just because it is in the box marked something does not magically make it that. I would guess that some portion of NWA stones sold as a certain find are not. If they are never cut then no one will ever know for sure. I have a pile of stones from a batch of several hundred NWA 869 that clearly are not NWA 869. They just don’t match all the requirements and I have set them aside. We will have to wait until they are cut to learn more and see if they actually are part of that tremendous fall. If they are not and are stones from overlapping strewnfields in the area of NWA 869 or are just other meteorites thrown in the box by the gatherers in the desert, they must be sold as Unclassified NWA stones.

It was a little more common a few years ago to buy big batches of stones, like a crate of Al Haggounia 001 or twenty kilos of NWA 791. Those two are easy to identify, even before cutting. But telling the difference between many of the other old falls not so easy. No one is going to have much of a problem with identifying a Millbillilli stone. They look a certain way, are coated in the orange soil, they are very distinctive. But, that is not the case with old desert finds where the boundaries of the strewnfield are sort of known to the gatherers only and locations are not recorded for the pieces found. To add to the problem the stones pass through many hands before arriving at their final owner.

At gem shows the stones are in boxes sort of graded into price ranges. This seems to be based on their general state of weathering as seen by their exterior. The fresher ones are pulled out and put inside the suites or on tables while the older stones remaining in boxes. I am a lifetime swap meet junkie and have little compunction about just digging into a box of meteorites and combing through it for a treasure missed by others. But over the years thousands of hands lift them, handle them, and then put them back into maybe a different box. After a few years, they are completely mixed. I bought a strange stone a few years ago from such a box. I wrote the story and won’t repeat it here. But it turned out to be a beautiful impact melt. I have described it to friends over the years and on two occasions friends have said I have a piece of something just like that. And I am sure they do. I don’t think we really comprehend the level of chaos that exists in some portions of the meteorite stream from finding to final owner. Yet we do the best we can, trying to abide by rules of provenance and curating. But it is often at the saw that the evidence of poor collecting practices and mishandling in the distant past is revealed. For me lately, the discovery that stones were not what they were believed has been great fun. These revelations have occurred at the beginning of the process and provided me with some excitement while also bringing several new classified meteorites to the world.

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