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25.6 grams. 80 x 60 mm.   Achondrite-ung

TKW 2.84 kg. Fall not observed. Purportedly found near Aougrout, Algeria. Purchased February 2023.


 

Steve writes:

NWA 15915 is an interesting ungrouped achondrite meteorite. While lacking in olivine and plagioclase, it exhibits a crystalline structure with inclusions of discrete enstatite grains and accessory alabandite, daubréelite, low-Ni kamacite, sulfides, and troilite (this description is from the MetBul – I don’t even know what half of these are, let alone how to recognize them!).

Last year, Scott McGregor posted some nice pictures of his slice of this meteorite (MPOD 230915 from Tucson Meteorites). His reply to one of the comments noted that he later regretted passing on an end cut of largest stone from this fall; I had followed with a note describing how I had acquired both a slice (18.8 grams) and an end cut (48.3 grams) from a smaller stone and would post images when I had a chance. Sorry it took so long.

Photos 1 and 2 show the end cut (the slice looks much like the polished surface of the end cut, so I didn’t bother to include a separate photo of it). Videos 3 and 4 offer 3D projections of the crust in two interesting areas: the first shows angular crystals, while at the upper left of center in the second video, one can see a translucent crystal with several of the aforementioned inclusions inside.

Photo 5 is an animated GIF comparing a back and front lit area of the end cut’s crust that exhibits some translucent crystals (the end cut is approximately 13 mm thick there, with the backlight applied to the cut surface and the photograph taken of the actual crust). Video 6 offers a 3D projection of this region with a small amount of front lighting to help illuminate the area around the translucent crystals. Videos 7 and 8 blow up Video 6’s center and left areas, respectively (the views were rotated some to best fill the video frame with the translucent regions). And Photo 9’s animated GIF shows the same area, but from the cut side (with the backlighting now applied to the crust).

Personally, I find the aforementioned crystal inclusions particularly intriguing. Photo 10 alternates between a front and back lit area of the slice to show a typical translucent spot (in the front lit image, the different accessary minerals are evidenced by their variations in colors and shapes). Of note is the tendency for the darker areas in the front lit image to demonstrate some of the greatest translucency (as seen when backlit).

For those that can view 3D crossed-eyes images, Photo 11 shows how these accessory mineral inclusions can vary in depth through the parent diopside crystals (although rotated, it depicts the large translucent crystal just right of center at the top of Photo 10). Photo 12 is included for those that favor parallel eye viewing. And for those with red-cyan 3D glasses, Photo 13’s anaglyph provides an additional way to view this area. But while the depth of the inclusions is much harder to appreciate, for those that can’t view any of these kinds of images, Video 14 offers a 3D projection of that same backlit area, with Video 15 taken from the opposite angle and with the addition of some front lighting (the latter also makes evident the different kinds of crystal inclusions per their shapes and colors).

Finally, while iron-depleted enstatite in aubrites like Norton County or Pena Blanca Springs fluoresces, most of my meteorites don’t intrinsically demonstrate this effect (though fluorescent terrestrial caliche does sometimes infiltrate weathered meteorites – typically between cracks or around the outside – and even occasionally phosphoresces). Yet as seen in Photo 16’s animated GIF, the meteorite appears to uniformly fluoresce a deep red color when lit with a strong (15 watt, in this case) 365 nm UV light (the numerous bluish features in the UV frame are likely residual polishing compound embedded within the tiny fractures inside and between crystals in this slice). That said, I can’t say whether all of the crystals are fluorescing or whether the more translucent crystals are only passing the red fluorescence of the surrounding opaque crystals – either way, it’s different than I’ve seen in my other meteorites.

When I acquired these pieces, I was told that Dr. Tony Irving was planning on doing some additional studies of this material – if so, maybe we’ll get a better understanding of some of the more unusual characteristics of this interesting meteorite.