— March 29, 2021
In the foreground of this photo, at The Box rock climbing area near Socorro, is a basalt lava flow that has a brown varnish. A fresh piece of the rock is shown on the smaller photo below, with a penny for scale. This is the basalt of Broken Tank, which flowed into the area from the south about 8.5 million years ago. This lava has interested Richard Chamberlin, who mapped it out, and myself for many years because one can use it to infer paleo-slopes and paleo-geography at this time period.
But recently I found out another intriguing fact about this basalt: a piece of this same outcrop is now on Mars! Of all the rocks out there, a sample from this outcrop (maybe not exactly the place below, but close to it) was chosen as an onboard reference standard (monitor) for the Alpha Particle X-ray spectrometer instrument on the Curiosity Rover ( http://msl-scicorner.jpl.nasa.gov/Instruments/APXS/). The rock was chosen because it is aphyric (lacks out-sized large crystals); also, it is very hard because of a peculiar interlocking texture of these crystals. So the rock hardness means it can survive the launch without cracking, and the uniform, fine crystal sizes means the instrument can zap any part of the standard rock and have uniform chemical readings. Pretty cool to have a piece of Socorro sitting on Mars!
For more information, Richard Chamberlin did a nice write-up on the rock is found in our journal, New Mexico Geology (vol. 33, no. 2, p. 40-41).
— Dan Koning,, Sr. Field Geologist, NMBGMR