Photos of my strange UNWA stone, cut in half
Posted 23 February 2009 - 08:11 PM
I got my strange UNWA back from cutting today. It has been cut in
half and the inside is finally revealed. First, a little backstory
to explain what caught my eye.
On the outside it looks like a million other weathered UNWA
stony chondrites. But notice the shiny "veins" that are revealed
on the surface of the specimen. They look different than the
rest of the stone. At first glance it could be remnant fusion
crust, but it's not. It appeared to be a vein of metal or oxidized
metal, or glassy shock/melt material that weathered slower than
the rest of the specimen. It should also be noted that the
specimen is strongly attracted to a magnet.
On the interior, several features stand out -
1) the matrix is similar to Al-Haggounia 001. It looks like
enstatite, but upon closer inspection it appears to be some
form of more familiar chondritic material. It has prolific metal
grains, but they are very tiny. Most of the metal flecks I have
seen in UNWA OC's is more coarse grained - the metal in this
meteorite is much finer, and is only apparent as a general
glittering when held in the hand and turned under a light. The
metal grains are not easily discerned until you see them with a
10x loupe. The matrix is a deep brown to light tan with black
grains that contrast the sparkly metal and enstatite-like pale
2) There are numerous veins that run through the matrix like rivers. In fact, they resemble a large river delta as seen from a satellite photo. They appear black when looked at straight on, but are very reflective/shiny when held at an angle - like fresh pencil graphite on glossy black paper. The veins are attracted to a
magnet and appear to have stronger attraction than areas with
little or no veins.
3) there are a few faint relict chondrules and one large obvious
chondrule. The large obvious one is white and is located near
one edge. There are also a few distinct grey chondrules that are
very small and can be seen in the close-up photo I posted - they
are located very close to the large white chondrule, between
the white chondrule and the edge of the specimen. There is also
an apparent black chondrule nearby. Otherwise, chondrules are
not seen in the majority of the matrix. Chondrules are mostly
present in the areas of the matrix where the veins are sparse or
4) there is no noticeable or distinct border or dual lithology - the differences between the chondritic portion and the EL-like portions of the matrix are subtle.
After looking at the photos and reading this description, would
anyone care to guess what petrologic type it might be? Any
observations or comments would be appreciated. Is this a shocked
OC with glassy/melt veins, or is it some kind of EL-type meteorite related to the Al-Haggounia/NWA 2828 types? Or is it some kind of highly-oxidized transitional chondrite with mesosiderite-like features? Does it contain Andromeda strain?
Link to the gallery of photos -
Links to individual photos -
The whole stone (notice the "veins" ??) - http://i268.photobuc...nwa-weird-1.jpg
Another photo of the whole stone - http://i268.photobuc...nwa-weird-2.jpg
Closeup of the matrix and "veins" (notice the big white chondrule and smaller grey/black chondrules nearby) - http://i268.photobuc...d-3-close-1.jpg
Both halves showing the matrix - http://i268.photobuc...rd-halves-1.jpg
Exterior, showing the "veins" - http://i268.photobuc...eird-vein-1.jpg
Another interior matrix shot - http://i268.photobuc...eird-vein-2.jpg
Another interior photo showing the veins - http://i268.photobuc...eird-vein-3.jpg
Photo of the veins reflecting light at an angle - http://i268.photobuc...n-reflect-1.jpg
Thanks for taking a look!
Posted 24 February 2009 - 10:24 AM
I wonder if the melt is instead shock veining. And if the relic chondrules are just heavily metamorphosed as in high numbered chondrites. Relic is a word than carries with it plenty of additional implications.
With weathered stones, it takes meteorite inspection to a whole new level. Like ancient bones from extinct critters, these weathered meteorites amplify the challenges to identify features commonly used in basic classification.
Posted 24 February 2009 - 11:27 AM
The pics are extremely interesting and has my curiosity built up.
Though,with individuals like Martin looking over the pics,theres a good chance things will be seen that may have escaped others eye.
Posted 24 February 2009 - 01:23 PM
I love UNWA,s, there is so much mystery behind them.
I have several UNWA,s my self,one weighs 4090 gr., and was wondering if it is possible to get a saw for our purpose. All the saws I looked at were way to big to use for the hobby aspect.
Did you consider buying one for your self? I noticed you had to send yours out for cutting.
Posted 24 February 2009 - 03:34 PM
A little more information....
One of my wholesale sources is a very knowledgable collector and is very experienced with classifying stones - he has several dozen specimens of his own that are classified. Along with our own Martin (Zagami), I consider his opinions to be authoritative. He saw my photos and heard my description, and I will summarize what his opinion here :
He thinks it is a highly-weathered ordinary chondrite, probably an H5 W4. He said the veins were not originally present in the meteorite and are the result of long-term terrestrial weathering, presumably moisture seeping in along existing fractures to penetrate the meteorite - and forming the veins of oxidation products.
So, he thinks the veins are oxidation products from terrestrial weathering. I am still not convinced, because it's notoriously difficult to identify a specimen based solely on photos without firsthand examination. I disagree because if the veins were the result of weathering, then I would assume that oxidation would not produce a substance that is glassy and weathers slower than the rest of the unaffected matrix. So, I doubt oxidation products would be left in relief on the external surface of the meteorite as the rest of it weathers away into nothing. To me, this looks like something that was present in the meteorite before it weathered.
I asked several other people and am waiting to hear back with some more opinions.
Yes, "relict" chondrules was a poor choice of words since it conveys a specific definition that is probably not met in this example. I should say the chondrules are faint and not well defined.
Typically, if these veins are from shock, what are they composed of? I assume it's material from the matrix that has been altered due to extreme pressure and heat, so what exactly is the vein material now?
Regards and clear skies,
Posted 24 February 2009 - 04:37 PM
I have trouble with the terrestrial formation of the veins, but have no problem with terrestrialization causing its current look.
The difference between a melt and those features of shock are somewhat subtile. Here is some info to digest. First, as paraphrased on Jeff K.'s site Meteorites Australia:
"Depending on the pressure it will affect these meteoroids (later to become meteorites) in different ways. More lightly shocked meteorites may just display dark shock veins running through while the Impact Melts will display a melted and deformed matrix. The information below is derived from studies presented by D. Stöffler et al. (1991)."
And here is the link to Stöffler's article to read yourself if interested. Stöffler's article
I don't see the deformation in your piece, just the veining. Also, they seem to radiate from a starting points and remain fairly thin.
I hope you don't mind, but I posted your excellent photo below to aid in this discussion. Just let me know if you want it pulled.
The photo below is owned by MikeG.
Posted 24 February 2009 - 07:23 PM
Posted 27 February 2009 - 10:50 PM
But, I was reminded, by a fellow collector, of the following webpage that details the Al-Haggounia strewnfield and meteorites -
Scroll down and look at the photos in the article. Notice how some of the more weathered specimens have veins exactly like my stone. Although I don't have a lab and I cannot formally classify or pair this stone as Al-Haggounia, I am confident that the mystery has been solved. So I am not going to send this stone off for classification. Instead I will keep half of it (because it is attractive aesthetically to me) and dispose of the other half.
This identification mystery was fun and educational for me - it goes to show that sometimes the answer is sitting right in front of us, but we refuse to see it.
Regards and clear skies,
Posted 28 February 2009 - 06:39 AM