In this post, we delve into the specific instruments used in the lab for mineral analysis. The audio is a bit choppy because we recorded about 90 minutes worth of audio, so I had to cut it down to a reasonable time-frame.
We're moving beyond basic mineral identification, which you can do with a simple geology kit. Instead, we're diving into the quantitative methods we use to study minerals. This involves using specialized instruments in our lab, though there are many other tools out there. We're focusing on the instruments we're most familiar with since we have a good selection right here in the lab.
We're currently working on a few projects that show the practical applications of mineralogy. Our Prospering Backyards project is investigating how zeolites can absorb toxic lead from soils. This ion exchange process is spontaneous, needing only water, with no additional energy needed. We’ve had great results, lowering lead levels in almost all yards tested to below five parts per million. This project was started as an art-science collaboration through the Getty PST project. Part of the artwork is to take the treated soils, press them into pellets, and create beautiful mosaics. Two of these mosaics are on display at Cal State LA and it’s open to the public. See this great write-up by LAist.
We're also involved in a Getty PST project, collaborating with the Pacific Standard Time art initiative, including a project with LACMA on pigments and the colors of paintings in their exhibit “We Live in Painting.”
In other news, we've been following a significant lithium deposit found in southwest Arkansas. This is exciting because the U.S. is currently very dependent on other countries for lithium. This deposit may lead to U.S. lithium independence, which is crucial since lithium is in high demand for batteries in electronics and electric cars. Some of the research that I’m conducting is to find ways to improve lithium extraction directly from brines using minerals, making this discovery particularly exciting and relevant to my work.
In this podcast and post, we delve into the specific instruments we use in our lab for mineral analysis. I recorded a video of the lab before we did the audio recording (it’s at the bottom of this post), so I may have skipped a few things in the podcast.
We start with optical microscopy, an older tool for studying minerals, but still important for observing crystals. Even though it is an older method, it remains the preferred method for analyzing asbestos using polarized light microscopy (PLM). PLM is a technique used to study minerals by shining polarized light through thin slices of the mineral sample. As light passes through, it interacts with the crystal structure, revealing properties like color changes, brightness, and interference patterns. These features help identify minerals and understand their composition and formation. The method is widely used in geology to examine rocks and minerals and gain insights into their history and the environmental conditions in which they formed.
Next up we have X-ray Diffraction (XRD), which is the gold standard for determining the atomic structure of minerals. XRD is used in many scientific fields. In the podcast, I use an analogy to get a sense of how XRD works—of slicing raisin bread, showing how the technique measures the planes of atoms within a crystal. In the podcast I said that the first crystal structure was determined in 1918, and I was close, but it really was 1913 and the Bragg’s solved the structures of halite, sylvite, diamond, and KBr. Here’s a video:
We use XRD to identify new minerals, study how minerals react in the body, work with companies to develop drugs, and find better ways to extract lithium. We can even use XRD to study the structure of liquids, including salty waters that some bacteria love to live in, and how that can help in the search for life on other planets. Below is an interview I did with the Adventure Club—be warned, it’s an hour long and I probably misspoke on some things :) It’s hard to remember to say everything correct in the heat of the moment when you feel the pressure to keep your words as short as possible! But I digress…
We can also perform a type of XRD called pair distribution function analysis, which is used to study the structure of liquids, albeit, the very short range ordering that occurs in liquids (2 Å to 15 Å, or so). This technique is particularly useful when you want to study how fluids begin to arrangement themselves right before crystallization.
X-ray Fluorescence (XRF) is another tool we use, which identifies the elements present in a sample by analyzing how they fluoresce x-rays when excited. In the Prospering Backyards project we use XRF to measure lead levels in the soil and the zeolites. It can also be used to create detailed maps of elemental distributions across a sample.
Raman Spectroscopy, a laser-based technique, analyzes the symmetry (and distances) between atoms and their bonding. We use Raman spectroscopy to study crystal growth, design new materials, and identify microplastics in fish guts. We're also using it to identify the source of black carbon particles trapped in bird feathers as well as black carbon trapped in minerals. It’s an extremely versatile technique and probably the most used instrument in the lab.
A Scanning Electron Microscope (SEM) uses electrons to image samples at very high resolutions. It can also identify the elements present in a sample. Samples are often coated with a conductive material such as carbon or gold to improve imaging. In mineral sciences at NHMLA and in collaboration with UCLA, we use SEM to study the morphology and elemental composition of kidney stones.
Finally, Laser-Induced Breakdown Spectroscopy (LIBS) uses a powerful laser to turn a small part of the samples surface into a plasma. It then analyzes the light emitted from the plasma to determine which elements are present. LIBS is especially useful for identifying lighter elements like lithium. It’s not as quantitative as some of the other techniques, but where it lacks in precision, it makes up for in so many other ways: low detection limits, zero sample preparation, can analyze solids/liquids/gasses, and so much more.
This podcast is really an introduction to the different ways minerals can be studied. In future episodes, we plan to take a deeper dive into specific projects and topics.
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