The environment between tree tops and deep bedrock where earth, air, water, and an array of living organisms interact is called the critical zone. Critical zone observatories (CZO) are site that are designed to study biogeochemical interactions that occur in time scales from seconds to geological millennia and spatial scales from microns to kilometers. The CZ is important to many terrestrial life, especially humans; however, the physical and chemical properties and their function are not always well characterized. In particular, CZ science is challenged to accurately quantify mineral assemblages that occur in the subsurface. Soil quality in terms of nutrient capacity and water availability are closely related to the parent rock material, which weathering process act upon. X-ray powder diffraction and thin section analysis are common approaches to quantifying minerals. Although the techniques are based on different principles, the quantitative results should agree. It is hypothesized that the two methods will agree in outcome, given assumptions about mineral stoichiometry. To test this hypothesis, thin sections were analyzed with an electron microprobe. Three samples were collect from the deep Mary Lou aggregate quarry to provide a basis to evaluate unaltered parent rock. Results are intended to highlight the differences in each approach and reconcile the inadequacies between the techniques. Reconciling these differences can lead to understanding the range of mineral composition variation in both small and large landscape scales.
Cannida, Tyler (2018): Petrography of the gneisses from the Mary Lou Quarry in Clinton, SC: Implications for quantifying mineral compositions in the critical zone. Center for Undergraduate Research Opportunities (CURO) Symposium, University of Georgia, Athens, 9 April 2018.
This Paper/Book acknowledges NSF CZO grant support.