A few of you may have seen my excited tweets over the weekend about my very first meteorite. I never intended to buy one, but I found a rather handsome specimen that fit my college student budget. One of the grad students that works at the Cascadia Meteorite lab on campus referred me to Rob Wesel of Naklha Dog Meteorites which is outside of Portland in the suburb of Hillsboro. After perusing his collection and drooling over a few pretty pallasites whose cost could keep me feed for a few months, I decided on an enstatite chondrite from Northwest Africa, NWA 2965.
An enstatite chondrite is basically a meteorite that is comprised almost exclusively of the mineral enstatite. I wrote a little about this mineral here in relation to its position on a ternary diagram. Enstatite is the magnesium rich end-member of the mineral pyroxene (MgSiO3). In other words pyroxene is the general mineral name and enstatite is the classification based on the high amount of magnesium found in that crystal. As far as chondrites are concerned, these are considered the rarest class (1).
My first thought was that it didn’t look much different from any number of the weathered basalt found in the area. It displays quite a bit of oxidation and what looks to be a precipitate, or mineral growth on the outside. From what I’ve read about its history, this is to be expected. This little piece of cosmic history was recently unearthed from a dried out lake bed, or playa, in Morocco (or Algeria, depending on the source) in 2005 (2). A playa is a good source of alkali salts which would explain the precipitate features on my portion of meteorite.
According to carbon-14 dating, this one has been a terrestrial resident for approximately 23,000 years (3). Some sources I’ve read have put that as one of the oldest earth dwelling meteorites found. All that time on the earth has meant that extensive weathering has occurred throughout the meteorite where the metals oxidized and precipitates began to fill in the cavities of the structure. This gradual replacement of non-earthly material with that of terrestrial minerals has helped classify NWA 2965 as a fossil meteorite.
1. Hutchison, Robert. Meteorites: A petrologic, chemical, and isotopic synthesis. Cambridge University Press. 2004.
2. T. Bunch and J. Wittke, Northern Arizona University; A. Irving, University of Washington. http://www4.nau.edu/meteorite/Meteorite/Al_Haggounia.html