You know that moment in life when you stumble across an idea or an object that incapacitates your words and thoughts? When you know that you’re looking at something truly unique that few have seen? Having the chance to photograph this thin section was one of them.
A shergottite from the Cascadia Meteorite Laboratory. (Image taken by author)
You see, this meteorite is a piece of martian basalt. Normally, neither one of those words would excite me. Basalt just bores me and Mars is an overhyped, rusted out piece of the same rock (blasphemous, I know- may the space gods forgive me). But this, this was a plastic slip-case covered piece of the Red Planet in the palm of my hand. To say it was a humbling experience would be an understatement.
Shergottites are mafic to ultramafic in composition. For the non-geology folk out there, this simply refers to the mineral composition of the rock. Think of mafic as being shorthand for high in magnesium (Mg) and iron (F). These rocks are predominantly made from minerals that crystallized at great depths in the martian crust. Such minerals would include olivines, pyroxenes and some plagioclase.
In the case of this shergottite, we’re looking at all three minerals. The opaque minerals are mostly pyroxene with some olivine and the transparent ones are a type of plagioclase called maskelynite. This mineral is really neat because it looks like glass under different microscopic views, but it’s chemical composition betrays it as a member of the plagioclase family. The current hypothesis is that maskelynite recrystalizes from plagioclase after being subjected to high pressure in a very short amount of time. These conditions are created from large meteorite impacts that generate shock waves and melt the plagioclase. Consequently, maskelynite has been found at impact craters on earth as well (1).
If you’re curious and want to learn more, I highly recommend checking out the website for the Northern Arizona Meteorite Laboratory. They have some gorgeous images of shergottites along with other meteorites. The information can get kind of technical because it contains the chemical breakdown of the minerals, but there’s still quite a bit that’s understandable without a science background.
Glacial Till 