An Article In Meteorite-Times Magazine
by Tom Phillips
NWA 5000 (Lunar Highlands) Thin Section in Cross Polarized Light
Adam Hupe and Jeff Krosschell had enough faith in me to trust me with what (at the time) was the only NWA 5000 thin section. I can't express my thanks enough!
Dr. Irving was working with the thin but it was between examinations so he sent it to me. What a pleasure it was examining this material and to be able to discuss what I was looking at with Dr. Irving.
The first thing I noticed was the glass. Dr. Irving informed me that technically, glass is not a solid but a super cooled liquid, and that this glass in NWA 5000 probably was produced by ancient impacts into the dominant gabbroic rock on the Moon long before the final impact ejection of this meteorite.
In this glass were lots of tiny bubbles. I showed my shots to Dr. Irving and he said these bubbles are called vesicles, and they are the result of solar wind, trapped in glass. How cool!!!
This classification information is from The Meteoritical Bulletin
Northwest Africa 5000
Find: July 2007
Achondrite (lunar, feldspathic breccia)
History: Found in July 2007 in southern Morocco and provided to Adam Hupé in October 2007 by a Moroccan dealer.
Physical characteristics: A single, large cuboidal stone (11.528 Kg) with approximate dimensions 27 cm by 24 cm by 20 cm. One side has preserved regmaglypts and is partially covered by translucent, pale greenish fusion crust with fine contraction cracks. Abundant large beige to white, coarse grained clasts up to 8 cm across and sparse black, vitreous clasts up to 2 cm across (containing irregular small white inclusions) are set in a dark gray to black, partially glassy breccia matrix. One partially eroded clast exposed on an exterior surface contains both the coarse grained beige lithology and the more resistant black, vitreous lithology in sharp contact.
Petrography: (A. Irving and S. Kuehner, UWS) Fragmental breccia dominated by Mg-suite olivine gabbro clasts consisting predominantly of coarse grained (0.5 - 2 mm) calcic plagioclase, pigeonite and olivine with accessory merrillite, Mg-bearing ilmenite, Ti-bearing chromite, baddeleyite, rare zirconolite, silica polymorph, K-feldspar, kamacite and troilite. Some gabbro clasts have shock injection veins composed mostly of glass containing myriad fine troilite blebs and engulfed mineral fragments. Black, vitreous impact melt clasts consist of sporadic, small angular fragments of gabbro and related mineral phases in a very fine grained, non-vesicular, ophitic-textured matrix of pigeonite laths (up to 20 microns long by 2 microns wide) and interstitial plagioclase with tiny spherical grains of kamacite, irregular grains of schreibersite and rare troilite.
Mineral composition and geochemistry: Gabbro clasts: plagioclase (An96.1-98.0Or<0.1), pigeonite (Fs32.0-64.5Wo6.7-13.1, FeO/MnO = 51.1-62.0), olivine composition varies among the different clasts with the following values: Fa23.9-24.2, Fa40.4 and Fa58.8 (with FeO/MnO = 81-100), chromite (Cr/(Cr+Al) = 0.737, Mg/(Mg+Fe) = 0.231, TiO2 = 5.9 wt.%), ilmenite (4.1 wt.% MgO). Bulk composition (R. Korotev, WUSL): INAA of 6 subsamples gave mean values of 5.3 wt.% FeO and 0.4 ppm Th. Oxygen Isotopes: (D. Rumble, CIW) Replicate analyses of a gabbro clast by laser fluorination gave δ17O = 2.601, 2.684‰; δ18O = 5.014, 5.033‰; Δ17O = -0.036, +0.037‰.
Classification: Achondrite (lunar, feldspathic breccia).
Specimens: A total of 40.2 g of sample, two polished mounts and one large polished thin section are on deposit at UWS. Mr. A. Hupé holds the main mass.
Before you look at my pictures, check out Adams photos of the largest Lunar meteorite slice.
This is taken from one of Adam's Meteorite List posts and it nicely explains how cool this display slice is.
"I promised some images of the only complete slice taken from NWA 5000, "The Cosmic Masterpiece." The surprise is that a hermetically-sealed display system was manufactured specifically for this slice and is a one-off. We would like to take this time to express our gratitude to Steven Domonkos Sr., Sr. Research Engineer, Department of Atmospheric Sciences, University of Washington who fabricated this fantastic display system. Not only does it act as a display, it also operates as a preservation chamber holding a vacuum, which can and will be charged with nitrogen.
Although it may resemble something imagined from a Jules Verne book, it is a meticulously-created machine built to aerospace standards. The tolerances are incredible and the workmanship is exquisite. The frame was machined so precisely that it actually touches the slice at three points along the inside of the ring. The front and back are made from a bullet-resistant material that will not yellow over time. The synthetic o-rings are made of a material that will not degas, harden or decay. The valves and monitoring gauge are superb. Please ignore the base in the third image; it is a mock-up until a permanent one can be created. It is still a work-in-progress that has passed all pressure testing and will be ready in time for its inaugural public viewing at the 39th Lunar and Planetary Science Conference in Houston this March.
Even though lunar material is among the most robust meteoritic material available, these extra steps were taken in order to ensure that future generations will be able to experience NWA 5000 the same way we have long after our team has passed on. We went as far as machining extra parts so that the future stewards of NWA 5000 can maintain its pristine condition for perhaps 1,000 years and then hopefully another system will be in place."
The solar wind Vesicles are found in the glass and the trouble with this glass is it is nearly completely isotropic. What that means is, when you use cross polarized light, the glass is black and these black dots (Vesicles) against a black back ground are hidden. So in standard full Xpol, they would be easy to miss.
Please keep in mind I usually include the only most beautiful images for a Micro Vision post but this material is so interesting and important I also included many less attractive shots that I found to show unusual features.
For example, these shots were taken in incident (reflected) light at a magnification of 345X. This shows what the material really looks like. This technique will show the vesicles as white while the background is black.
I know these shots are ugly. For those of you who have worked with Xpol you might appreciate the difficulties associated with getting good photos of material that looks like this. (It gets better!)
Just for fun I took a few shots in DIC (Differential Interference Contrast). No great discovery here but still cool!
OK, now that I have shown what the vesicles look like in reflected light, lets see some Xpol. I start out at 85X. This is not in my preferred magnification range but it gives a nice perspective of size. Look how the glass appears to be a river current frozen in time.
160X is where I start to get dialed in. This set is a mix of material and not just the solar wind vesicles.
This set was taken at a magnification of 400X in incident (pass through) cross polarized light. Some of these shots utilized the Play Station 3 Quarter Wave Plate that I wrote about in a previous Micro Vision. It was difficult to show the vesicles nicely with out having the glass matrix as an intense color that would drown out the image. I set the polarizer to about 45 degree off extinction and the quarter wave plate to just a nudge off of full extinction. This allowed me to draw out color from mineral grains while keeping the glass relatively neutral.
Finally I take it up to 760X utilizing the same techniques as the 400X set.
This was the most fun I have ever had with a thin section! Paul and I have set up even more shots in my Micrograph Gallery so please check it out. Also, we have picked a few of our favorites and Paul set them up to be available on coffee mugs at the CafePress store. I can honestly say I highly recommend the mugs. They are a high quality with a brilliant image that does not fade with washing. Give one a try.
Tom Phillips can be reached by email at:
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