Rocks and their chemical constituents

The petrology and geochemistry lab houses several key tools and support equipment for the evaluation of rocks and minerals. The lab has a high-end polarizing light microscope and imaging system, as well as binocular and digital microscopes for evaluating the optical properties and surface features of rock fragments, thin sections, and mineral grains. Support facilities includes cleaning, heating, and polishing equipment.

Wavelength Dispersive X-ray Fluorescence

The lab is home to the KSG's Rigaku Supermini 200 Wavelength Dispersive X-ray Fluorescence Analyzer (WDXRF). This is a bench-top sized source and spectrometer that permits characterization of solid and liquid materials for elemental composition. The Supermini sends X-rays from a Pd tube to sample materials inducing secondary fluorescence. These secondary x-rays are characteristic of the sample's elemental makeup, which are then diffracted through one of three crystals into one of two detectors to determine concentration. The machine can be run in a scanning mode to determine qualitative concentration profiles or as a fully-calibrated quantitative analyzer.

The MSU WDXRF has been used to qualitatively assess minerals and rocks of varying composition, as well as the ions and sediment load of natural waters. It has also characterized whole-rock samples of silicic igneous rocks from southern Oklahoma, central Oregon, and west Texas. The instrument is introduced to students in upper-level and graduate coursework on minerals, rocks, and geochemistry.

X-ray Powder Diffraction

The lab houses the KSG's Rigaku Miniflex 600 X-ray diffractometer (XRD). This is a bench-top sized diffractometer that permits characterization of mineral powders. The Miniflex diffracts X-rays from a Cu tube through a powder sample; these are refined by a quartz monochronometer and collected with a scintillation detector as a function of incident-diffraction angle. The PDXL2 software is coupled with the ICPDD PDF-2 database to resolve the identity of powdered samples of single-phase materials (rocks and other solid media containing one mineral). Additionally, the software can determine the mineral and amorphous phase fractions in polymineralic materials, such as most rocks.

The MSU XRD has been used for identifying unknown mineral samples, but its chief use is resolving mineral concentrations and phase identification in granites and limestones. Current work focuses on improving Rietveld refinement techniques on assessing mafic silicate minerals and assessing weathering in granites.

Laser Induced Breakdown Spectrometer

The lab also contains a Laser Induced Breakdown Spectrometer (LIBS) for micro-sample analysis of earth materials. LIBS uses a powerful focused ultraviolet laser beam to ablate a small volume of a sample into a plasma. The light emitted from the plasma is collected and spread out (refracted). The elements in the plasma (from the sample and surrounding air) emit intense light at characteristic wavelengths. When the light is refracted, these characteristic wavelengths produce higher intensity peaks. These reveal the composition of the ablated material.

The MSU LIBS has been employed in characterizing feldspar and amphibole minerals from southern Oklahoma, gypsum from west Texas, and a number of other mineral and synthetic crystalline samples. It is extensively used in our  Mineralogy, Petrology, and Geochemistry classes. Current work focuses on data processing techniques useful to quantitative analysis.

Optical petrography and image analysis

The lab hosts equipment for optical microscopy, including capabilities for intermediate and high-resolution imaging. Standard dissecting and polarizing compound light microscopes are used to characterize Earth materials. Image capturing and scaling software, along with high-resolution flat-bed optical scanning provides detailed digital photographs. These can be processed and analyzed for particle size distributions, modal analysis, and geometric assessment.

The MSU optical petrography and image-analysis equipment has been used to characterize samples from all over the world. Studies continue documenting mineral populations in volcanic rocks from Oregon and west Texas, and microstructural analysis of granites from southern Oklahoma.

MELTS Thermodynamic Modeling

The lab also boasts a desktop running Ubuntu 18.04 LTS that can execute the powerful thermodynamic modeling program Rhyolite-MELTS 1.1.0 (Ghiorso and Gualda, 2015) - version built on  by Paula Antoshechkina. Thermodynamic modeling of igneous systems permits theoretical exploration of possible crystallization pathways using the bulk compositions of rocks.

The MSU modeling machine has been useful in constraining compositional and thermobarometric conditions on magmas from southern Oklahoma and central Oregon.

Affiliated tool: MCOSME SEM-EDS Facility

Our group relies heavily on compositional data. The XRF characterizes whole-rocks, but for evaluating materials on the grain scale, we use the scanning electron microscope (SEM) with energy dispersive spectrometer (EDS). The SEM permits imaging of microstructure for medium-rocks and fine-grained rocks. The EDS collects the electron-induced x-rays to semiquantitatively evaluate spot compositions, line traverses, and mapped regions of interest.

https://msutexas.edu/academics/scienceandmath/sem/