Searching for Impactite

Tuesday and Wednesday, Dec. 9 and 10

Since Ingrid and I finished our transects and David got his granite samples, yesterday the three of us decided to devote our time to search for impactite. This involved spending the better part of the day crawling over angular granite and rough ignimbrite gravel, searching inch by inch for small black, vesicular, glassy impact melt. The day got off to a slow start, since time seems to slow down a little when you’re not actually finding the rocks that you are looking for. The three us of picked up near the outer edge of a lobe of ejecta that Nathalie, Edmond, and Carlos had mostly covered the day before. We worked our way horizontally around the outside of the crater, and it quickly went from slim pickins’ to essentially no melt rock at all. We crossed over a swath of ignimbrite gravel that was completely devoid of impactite. After a reenergizing lunch break we continued on around the side of the crater, still hoping to find even one tiny piece of melt. We worked our way into a patch of granite gravel and suddenly I caught a glimpse of a little black rock that I knew immediately was the impactite we were searching for. As I leaned over to pick it up, I spotted another piece, and then another even bigger piece. Pretty soon all three of us were picking up melt rock left and right. The lobe had very distinct boundaries, and was small enough that its width was within the error margin of a GPS point in the middle. For the rest of the day we scoured this little patch for impactite, quickly filling a sample bag. Ingrid found many pieces in my footsteps, turned over as I walked up and down the slope. The ground was literally covered in impactite.

Sarah at Cerro Overo maar with Volcano Chiliques in the background

Today we picked up where we left off yesterday, this time with Nathalie, Edmond and Carlos as well. The latter three continued the search that we started yesterday in the lobe of ejecta we discovered, while Ingrid, David and I moved further around the crater to see if there were any more undiscovered ejecta lobes. Being the impactite picking experts that they are, Nathalie, Edmond, and Carlos had no trouble finding large pieces that we had missed the day before. Rumor has it that Monturaqui impactite sells for about 50 cents per gram on the internet, so if we weren’t so into science we could make a little cash off of our collection. There is geochemistry to be done however, so there are bigger plans for all these bags of rocks. Ingrid, David, and I found a few more pieces today, but nothing like the patch from yesterday. We finished the day a little early to have some extra time to rest up. After that much deserved break, and some delicious ice cream for dessert, we’ll be ready to go again tomorrow.

Sarah at Laguna Lejia with Volcanoes Aguas Calientes and Lascar (r to l) in the background