At last nights Skeptics in the Pub a very good friend of mine, Karla, gave me an unexpected gift: a small piece of a pallasite. These meteorites are what I like to call space rock bling and I actually wrote a post about them with the same title. Pallasites are a stony-iron meteorite that have a nickel iron body (or matrix) and are studded with olivine crystals. These meteorites are thought to represent the core/mantle boundary of a differentiated planetesimal that was impacted by another object and broke apart. The iron-nickel matrix is from the core and the olivine crystals are from the mantle. The pieces became incorporated during the impact much in the same way that you work chocolate chips into dough.
This is a piece of the Esquel pallasite from Argentina. It's considered one of the most beautiful due to its large olivine crystals. (Image from Wikipedia)
Mine is labeled as the Bela Pallasite, Russia, but I don’t have much information beyond that. Pallasites discovered in Russia include the Omolon, Pallosovka, and the Krasnojarsk. There was also one found Belarus called the Brahin. I’m not sure which of those mine could be from, but it’s one of the nicest gifts I’ve received in a long time. So, with that I want to say a big thank you to Karla! She made my evening with this piece of cosmic debris and also gave me the inspiration for today’s Meteorite Monday.
My own piece of pallasite! The 2nd piece in the middle has a somewhat visible olivine crystal in it. Bike key for scale.
Stony-irons are hands down the prettiest meteorites to look at. They’re somewhat similar to their iron meteorite cousins in that they have an iron-nickel body, or matrix. However, they are unique in that some are studded with these gorgeous olivine crystals called peridot. The accepted consensus is that these meteorites originated at the boundary between the core and the mantle of asteroids that grew large enough to develop such features (1). This is because peridot, a magnesium rich olivine, crystalizes at very high temperatures only found at the mantle. The stony-irons with these olivine crystals are called pallasites.
Esquel Pallasite from Ohio State University
The other type of stony iron is called a mesosiderite. These guys are really cool because their composition is thought to be the result of a collision between two molten asteroids. Mesosiderites still retain the iron-nickel body of the pallasites, but contain chunks of melted rock (clasts) instead of olivine crystals. The angularity and direction of the clasts is suggestive of a large impact between two asteroids, with material from the crust mixing into the iron-nickel core (1).
Mesosiderite from Arizona State University
1. Smith, C., Russel, S., Benedix, G., Meteorites. Firefly Books. 2009. P. 67.