Summertime at Caltech is usually filled with swarms of people bustling around campus, working away on research. The SURF program brings in students from far and wide who are all excited to solve problems and make new discoveries. But campus can be a bit crowded, right? So join me on my journey to the mountains to get away, pick up some rocks, and bring them back to the lab to make my own discoveries.
As a Geochemistry major, my focuses lay both in fieldwork and lab work. This summer, my research took me out to the mountains in San Diego County, CA, and into the Geology and Planetary Sciences (GPS) buildings on campus. Going into it, I didn’t expect my work to be a lot of physical labor. Who knew I’d be replacing the gym with my project instead? On the first day of the SURF period, I drove out to Pala, CA, to visit the Tourmaline King Mine to get an idea of the rocks I’d be working with over the summer. My project goal is to collect strontium isotope data for the rocks around this mine to better understand the geologic relationship between all of them. This first day involved a lot of walking around and looking at pretty gemstones. The owners of the mine let us pick through one of their gem screens and take home some that we liked.
Unfortunately, these pretty gemstones aren’t the ones that hold the answers to my SURF project’s main question. Next, I moved on to a different set of mountains, further south in Julian, CA. Here, I spent three days collecting rock samples from each unit (defined as each different rock type) to take back to campus. The main field work consisted of a lot of hiking, hammering samples out of the ground, and bagging them up. I’d say the longest hike took us seven hours round trip, and I was fighting exhaustion every step back to the car. Regardless, we collected everything we needed from the great outdoors and then began the long cycle of preparing each sample. Just before we left Julian, we treated ourselves to their famous apple pies. 10/10 would recommend. Moving onward to the rocks…
If I thought the hike was rough, sample prep was a good match for it on campus. I dragged each sample to the second basement of the lab and placed the large rock chunks onto a water saw (We’re talking at least ten-pound rock chunks). Then, each piece was cut down to manageable sizes (9 square inches or smaller) and any weathered surfaces were removed. After cutting, each piece was sanded down. This step helps remove sharp edges and cleans any potential contamination from the saw blade to the rocks. I then sonicated the samples to lift any remaining dust.
Remember how I said this project replaced my gym time? That part kicks in here during the sample prep phase. Every piece has to get crushed down into coarse sands and fine powders. First, the cleaned samples are hammered down into small bits. The hammering step makes me feel like Thor for the first two rounds, but the hammer gets heavier and heavier as the day goes on. There’s a metal stand and something that looks like giant metal bolt (without threads) that I set the rock between to help this step. Each one is hefty and adds to the muscle fatigue as I keep working through them. On my own, I can only get some of the sample into a powdered state, so I used a machine to finish the job. I call it the “jaw crusher,” two metal plates that smash the rocks into the powders I need. This process took weeks, as we collected 37 samples, and each one needed to reach this powdered stage.
The final steps to the sample preparation includes sifting the grains by size and allocating certain ones for mineral separates and whole rock analysis. Whole rock analysis is run through an X-ray Fluorescence instrument and gives us an excellent compositional profile. Mineral separates are the main target for my project. To take these separates, I had to place grains 500-250 microns in size into a Petri dish under a microscope and then pick out the individual grains for the mineral I want with a pair of tweezers. It’s as tedious as it sounds. But it has taught me some better tricks for mineral identification, so I suppose I learn something in each step. My grains were then mounted into epoxy resin mounts and are finally ready for analysis. A few have been put through their machines already, but not all.
By the time I was nearing the end of my SURF (around 8 weeks in), most of the samples were waiting for me to run them and collect data. I ran them through an electron probe to confirm the minerals I picked. Then, they underwent laser ablation mass spectrometry, which gives me the strontium isotope values. This step lasted the remainder of the summer, and I’m hoping I got some nice, realistic numbers to compare to work previous researchers have conducted in the area. I’m back on the crowded campus, but it won’t be bustling with SURF students for much longer. We’ll take a break, and then campus will blossom again with students once everyone returns, ready to tackle the year.
