UW Microprobe Laboratory

Yes, I know it has been quite a while since I’ve posted, but it is worth the wait!
These are polarized light images from a thin section of one of the world’s most iconic meteorites, Nakhla, the ‘N’ in SNC (S=Shergotty, C=Chassigny). These samples constituted an enigmatic group of meteorites that were determined (in 1988) to be from Mars based on the identical ratios of trapped noble gases in the meteorites compared to that found in the Martian atmosphere. There are now well over 100 meteorites believed to have originated on Mars.
Nakhla is an olivine-clinopyroxenite, and hence a cumulate igneous rock. It was observed as a fall in Egypt between 8:30-9:00am, on June 28, 1911, and consequently, the meteorite has not experienced any terrestrial alteration. Yet, it is known to contain the hydrous alteration mineral assemblage collectively known as “iddingsite’, replacing olivine, indicating that the hydrous alteration took place on Mars.
So, what is Nakhla doing in the probe lab? Retired Professor Bernard Evans has been on a search for Fe-rich olivine grains that have been altered at low temperature to hydrous mineral assemblages that include the unusual ferric iron-rich sheet silicate called Hisingerite: Fe+++2Si2O5(OH)4•2(H2O). See the link, below.
Because the hydrous alteration took place on Mars, the question was ‘Might there be hisingerite?’ In short, YES! We did find hisingerite in Nakhla. The study, cited below, suggests that terrestrial hisingerite formed from olivine at 100-200C during interaction with strongly oxidizing solutions. Presumably, these conditions also exist(ed) on Mars.

Journal of Petrology, Volume 58, Issue 3, March 2017, Pages 495–512
Serpentine, Iron-rich Phyllosilicates and Fayalite Produced by Hydration and Mg Depletion of Peridotite, Duluth Complex, Minnesota, USA. Bernard W. Evans, Scott M. Kuehner, David J. Joswiak, Gordon Cressey.

Sad times for the Probe Lab. Prof. Stu McCallum recently passed away and today was the celebration of his life. Former students, friends and family came to Seattle from locations around the world. Stu joined UW as an igneous petrologist in 1970 and retired about 2008. Stu hired me to run the Probe Lab 29 years ago. He was 80 years old.

This beautiful achondrite meteorite just arrived in the Probe lab and we've identified it as a new ANGRITE! Angrites are a most unusual group of achondites of which only 15 or so are known. Angrites are interesting for many reasons, one of which is that they are the oldest igneous rocks known in the solar system, up to 4.563 billion years old, meaning they crystallized just 10million years or so after formation of the solar system.

Characterization of meteorites via microprobe usually consistent of sometimes mundane routine analyses of the minerals olivine, pyroxenes, and plagioclase, with a textural interpretation of their interrelationships. Occasionally, you find something really cool, like here. This is a phosphorus-bearing iron nickel sulfide. This phase has not been found on earth, and of the more then 60,000 meteorites found on earth, less then 10 contain a P-bearing sulfide. There is at present, no name for this phase.

An amazing shock-melt and recrystallization texture in a martian meteorite. The circular 'blob' is composed of dark plagioclase laths, blocky olivine grains (brightest) and ortho/clino pyroxene (intermediate gray). The surrounding dark area is composed of about a zillian needles of plagioclase and much lesser pyroxene with rock v***r vesicles!

The blob is the residual melt after the plagioclase needles crystallized.

'Pseudo' metamorphic reaction in Angrite meteorite. Pseudo because the reaction is :

Olivine + Plagioclase + Liquid1 = Clinopyroxene + Spinel + Liquid2