As I cut meteorites to prepare them for sale I occasionally find one which is deserving of being classified. I would get them all classified if that was practical. But the realities of today are that ordinary chondrites are not being classified by many of the individuals who used to do them just 5 or especially 10 or more years ago. There are actually many fewer choices for us who find new meteorites or cut into a meteorite and want to get it classified.
Well I ran into three meteorites a while back that were nice or unusual. We bought all of them about eight years ago. One stone was the topic of my article last issue. That was NWA10731. Almost as that article was coming out I heard from Cascadia Meteorite Lab about the two others I had sent them. So they will be the topic of this article.
Paul Harris and I had a request from a customer for a large slice of meteorite to be used in public demonstrations and lectures. We did not have anything prepared that seemed to be near large enough. But we had a couple large stones we had never put in a saw. I chose the smaller of the two big unrelated stones for this customer’s slice. The largest stone has not been classified and likely will never be. But the smaller was nearly 7 kilograms and shaped like a rough sphere. Which made it about as hard to clamp in a rock saw as any stone can be. But I got a thick endpiece cut off and then took two more slices off. One of these was prepared for the customer with a polish on one side and the other side left at 400 grit to show off the structure a little differently. I noticed during that work that this was an interesting stone. It had occasional large chondrules of ¼ inch or more in diameter. It had little metal and was a generally fresh meteorite internally. No rust spots or staining just a beige colored matrix when it came off the saw. I knew it would darken some when polished they always do.
I did not do anything with the stone at that time as far as sending it off for classification. We sent off the large slice and the man was happy. We used a little of it for a couple more special orders. A customer was making marbles of meteorites and a piece was used for one of those one inch cubes we produced.
I was cutting into some other stones a year or so later and found two more that were not run of the mill ordinary chondrites. I decided that since I was sending off these two newly discovered interesting stones I would send off a piece of the big stone too. It was a nice meteorite and it would be a shame to sell 7 kilograms of pieces unclassified. Could I get someone to look at it was the question. The place I had been sending specimens to for 20 years was no longer doing ordinary chondrites. So off a chunk went to Cascadia Meteorite Lab along with NWA10731 and the other one we will get to soon.
You need to be patient in most things meteorite. When I began collecting there was no internet. Collectors waited for a price list to come in the mail from the few dealers that existed. We waited for something new to come on the market. It was not at all like the grocery store shopping we can do today. I had to be patient in collecting and I knew I would have to be patient later when I began getting them classified. It had often taken months in the past so I settled back to wait and find out what these three space treasures were. When I finally got information in an email on each one it is like another Christmas in the middle of the year. First, NWA10731 and then the big stone was finally done and on its way to the Nomenclature Committee for approval. I was looking at a summary of the data in my email and was very happy with the results. I knew it was not something really strange when I sent it, but to have it come back as an LL5 was nice.
At any one time in the last few years there are a few LL5s for sell. There are the favorites like Tuxtuac, and Paragould that can usually be found for sell somewhere. Then on rarer occasions truly historic pieces like Siena might become available. But even a search for more recent desert LL5 material does not yield a lot of returns. Oh, I can not forget the huge amount of Chelyabinsk that has blessed us the last several years, it is an LL5. But I was happy to be told of the classification since there are only a few available at any time. There are over 3,000 LL5 meteorites listed in the Meteoritical Bulletin Database but once you take out the Antarctic finds it is a much smaller number. And there remains after taking those away plenty of recent desert finds of LL5s but they seem to never be for sale. We now had a nice big supply and it was a pretty meteorite. It received a W2 for its weathering state and that confirmed what I had seen visually that it was nice and quite fresh inside. It had a touch of shock with a level of S3. The specimens I sent off for classification did not have any of the really big chondrules or if they did they were not exposed in the cutting of the pieces for analysis. I have done a great deal more cutting than the lab so I have run into a few of these giant chondrules. They are neat. I will rerun here a photo that I have posted before online of one about 7-8 mm across.
It is a really neat polysomatic barred olivine chondrule that was exposed by cutting and photographed on the surface of a slice not in thin section.
While most of the chondrules are small. The report in the Meteoritical Bulletin says 1-1 ½ millimeter chondrules are not infrequent. It adds a mention about 2 millimeter size chondrules being seen as well. But occasionally large slices have at least one of the much bigger chondrules.
The meteorite has a scattering of metal grains and there are no spots where the metal appears to have rusted out of the stone. There is no heavy staining of the ground mass and no brown spots around the metal. The classifiers have said there is 1-2 % metal in the stone. There are veins of hematite or magnetite running through the rock and the very large chondrules are usually rimmed in black mineral.
The official designation for this stone is NWA10816. There was a single mass which we bought and there is no information about any pairing that may exist with the many other NWA LL5s. This is a common situation with NWA meteorites. We will just never know for sure where most were found or by whom. The single mass weighed 6980 grams. I have prepared some very nice pieces for our catalog of NWA10816.
Just a few days after getting the results on NWA10816 we started to get some images from the lab on the third or our submissions. This stone was a single small stone that was very difficult to cut. I have dealt with friable stones before but this was way more crumbly than those. There was just no ground mass remaining in spots. The chondrules and small areas were simply floating in air mostly. As I cut the rock it fell apart into fragments. Cup shaped depressions were sometimes left behind when the chondrules fell out. It seemed as I was cutting that it was dissolving away into crumbs. Almost turning into a slurry of large fragments. I was to wonder later about a possible answer to this when the analysis was done. As I got a little deeper into the stone it got somewhat better. Clearly there was a thick rind on the outside of the stone that had weathered in a peculiar manner. The chondrules were medium size, well defined and colorful so my heart was breaking as the stone itself fell apart. I knew the meteorite was a low petrographic type. A type 3 or a 4 by the sharpness of the chondrules. As always I had my fingers crossed for a type 3, because I love them.
I took a couple large pieces from down inside which were holding together pretty well and sent them off. I thought there was something interesting and strange about the way it was weathering and that there was hardly any remaining metal. Later I was sent some images from Cascadia Meteorite Lab. One of which is shown below. The extensive amount of red in the image is calcium carbonate which has replaced the matrix of the meteorite. The light blue is iron oxide veins. I was told the image has one metal grain shown as the slightly darker blue. I can see one very small darker blue spot on the image I am not sure if that is the metal grain referred to or not. But the calcium replacement and iron oxide filling is fascinating. I am wondering now if the water coolant on the saw was not actually softening and dissolving the calcium carbonate adding to the crumbling of the stone. Though calcium carbonate should be quite resistant to the distilled or purified water I use.
I thought that it would receive a high weathering state and was a little surprised by the W3. But the stone does have portions with a light color and as it turns out between 5-10% of its original metal still remains. The report in the Meteoritical Bulletin describes the stone having void spaces and secondary replacement. The classifiers were able to get data from some of the olivine grains and determine the meteorite was an H chondrite. The chondrules appeared sharper than they truly were because of the way they were eroded out of the matrix. The stone presented some problems and to quote the classifier “The silicates are equilibrated, but the pyroxene is full of holes and inclusions, which will make getting the Fs content a bit tricky.” It was a type 4 which was still nice and in the range I thought originally. It is official with the designation NWA10828. Though most of the metal is gone from the stone it is still not as deeply rust stained as I would expect for one falling apart and with the ground mass replaced with caliche.
The center area of the single 541 gram stone may be easier to cut without crumbling as much. Though I do not know that for sure. The stone was broken in half and deeper down in the one half I cut it was better. The other larger half has not been touched yet and could be friable all the way through. I will have to find out. The surface I have to start with is still high fractured. I may try straight alcohol or cutting dry with my dust vacuum system on to prevent dissolving the calcium carbonate. Worth a try I think. We have kept all the fragments and got some larger pieces. We have them in our catalog. And I kept the smaller fragments and dust in a vial. Mixed in with the dust were small chondrules that fell out during cutting and handling. It is a pretty unique meteorite with the extensive calcium carbonate replacement surrounding many of the chondrules and the porous nature caused by all the void spaces.
Paul and I want to once again express our thanks to the staff at Cascadia Meteorite Laboratory for their efforts in classifying these two additional stones. Special thanks to Dr. Melinda Hutson and Dr. Alex Ruzicka.
I am doing an ever increasing amount of cutting and who knows what I will find in the future. Maybe the very next stone will reveal something strange and unique. If is does than I may be sending another piece off for classification and analysis.