r/meteorites

Polished seymchan pallasite from Russia

Alright, part 2.

First, we'll look at some more chondrites, a few polymict breccias, a few unclassifieds. Polymicts are cool because they capture multiple different lithologies that sample different depths in an asteroid. They tend to be kind of chaotic, high contrast stones. NWA 16382 is beautiful, not something I find myself saying about a lot of L chondrites.

I'll throw in a few impact melt breccias, one that looks like poop. Space loves poop jokes, true story.

Things get messy with the mesosiderites, winonaites, and IAB irons. Mesosiderites are all generated during impact events as two asteroids collide. One might have a rocky silicate surface, while the other is metal-rich. When they collide, they are both vaporized, shooting a spray of molten mixed material into space. As the molten droplets in this spray collide, cool, and recombine, they reassemble themselves into a rock, that's a chaotic mixture of metal and silicate. Winonaites are failed attempts at planetary differentiation. They got big/hot enough to start mobilizing metal, but were either disrupted early, or formed a little too late to be able to complete the job. They're rare types, but are associated with the same parent bodies as IAB irons. IAB irons themselves are very diverse, because even though they're from the same parent bodies, those bodies experienced multiple giant impacts, that mixed and created different lithologies in different places on the protoplanets. IABs are so complex that there are like 6 different subtypes, that all represent different physical regions on the same asteroid.

The Hickman is very pretty, but also very unstable, as it's got significant shreibersite/cohenite inclusions that are exposed to the surface, and got weathered pretty extensively. This stone is not long for this world, it's going to turn into a pile of rust eventually. It's really beautiful though, so I'll enjoy it while it lasts. Kinda looks like Venom.

There are a few ungrouped ataxites, Dronino and Gebel Kamil. Dronino in particular is a very weird specimen. It's an old fall that landed in a swamp, and is super nickel rich, so it rusted like crazy. You have to process all that rust away to get at the deep cores of these specimens that have not been corroded yet. As a result, you get this neat aesthetic appearance, where they kind of look similar to rocks that have been eroded by wind or water. The rust preferentially forms at boundaries between crystals, so in essence, when you strip away all the rust, you're left with a chunk of metal in the shape of the crystal structure of the taenite. It's sort of analagous to how they freeze and shatter Campos to break them along crystal boundaries, and turn them into a bunch of smaller meteorites, that are basically single crystals of metal.

NWA 13272 is WEIRD. It's an ungrouped achondrite, but chemically it aligns with L-chondrites, so it might be some kind of transitional specimen, capturing a chondrite as it's turning into an achondrite. Alternatively, it may just be an L-chondrite, that's been super-heated.

NWA 11640 is a beautiful ureilite containing some really nice olivine crystals, embedded in a pigeonite/graphite matrix. It represents the cumulate mantle material of a protoplanet that was rich in carbon. Think something like a pool of magma that slowly grows crystals that fall out of the solution, and drift towards the top, or bottom of the magma chamber. Those are cumulates, think of it something like ice crystallizing in the atmosphere, and then falling out to the ground as snow, creating fluffy piles, except this is all happening in a liquid magma chamber instead.

We end with the planetary achondrites, from the Moon, and Mars. The two lunars capture very different lithologies, from different parts of the lunar crust. The entire surface of the moon has been impact-gardened heavily for 4.5 billion years. As a result, it's been thoroughly shattered down to a depth of dozens of km. Almost everything on the moon's surface is a breccia, composed of particles that have been smashed to bits over, and over again, remelted, recombined, and smashed to bits again. It's very similar to Howardites from Vesta, actually, in a physical sense, albeit not a chemical one.

The martian meteorites are some of my favorites. There is nothing I enjoy more than dropping a piece of Mars into someone's hand, *before* telling them what it is. That wide-eyed realization of what they're holding is just priceless. Ouargla 010 is a great little piece, super aesthetic, just a killer example of a shergottite, but also very different from DAG476, the other shergottite, that formed within an extruding lava flow within ~1 meter of the surface of Mars, approximately 441 million years ago, where it sat for 440 million years before it was knocked into space by an asteroid impact. It floated through space for 1.1 million years before colliding with Libya. It sat in the Libyan desert for ~60,000 years until it was recognized as a meteorite, and collected.

Picked this up from azmeteorites! 1.16g

Amgala 001 26.014°N, 11.020°W

Saguia el Hamra, Western Sahara

Purchased: 2022 Dec

Classification: Martian meteorite (Shergottite)

Physical characteristics: Weathered exterior surfaces of the stones are brown with a distinctive knobby appearance. Fresh interiors are greenish-gray with darker olivine phenocrysts visible.

Petrography: Zoned olivine phenocrysts (up to 2 mm in length) are set in a groundmass with variable grainsize composed predominantly of prismatic, zoned clinopyroxene and lath-like maskelynite, together with accessory alkali feldspar, pyrrhotite, ulvöspinel, chromite (with variable Ti content), ilmenite, baddeleyite and chlorapatite. Thin opaque shock veins crosscut the specimen as well as secondary calcite veinlets. Olivine phenocrysts contain small patches of alteration products (red-brown in thin section).

Classification: Shergottite (olivine-phyric)

I live in Nebraska (this meteorite is not from here). Does anyone know where I can take this 15lb meteorite to be examined to get more information about its type and where it might have come from? I'm thinking maybe Morrill Hall Museum at UNL?