This is of great value to me. I'm currently studying geoscience at a university in Germany and even as a German I find this flood of terms and definitions way easier to understand in English. But it's not just that. Even the information itself and the way it is presented is so much more understandable than in my classes. I've also been enjoying your videos on thin sections a lot. I put them into my own digital atlas and they helped me a looooot. Thank you very much for uploading these videos! PS: Do you also do thin section analysis of carbonates and sandstones? I had a course on this, but I cannot remember the immense amount of micro fossils very well.
Thanks for your kind words. I'm so happy to know these benefit people outside the US. I've been spending some time trying to find good examples of chemical and clastic sedimentary rocks, and plan to make videos on them, too. But because I don't teach sedimentology or stratigraphy, it's been a lower priority than for igneous and metamorphic rocks (which I do teach). Your interest raises the priority on sedimentary rocks, though, so thanks for emphasizing them.
Nesse (2000; "Introduction to Optical Mineralogy") and Tröger (1979; Optical Determination of Rock-Forming Minerals; re-authored by Bambauer, Taborszky, and Trochim) describe several methods that use the index of refraction (anorthite is higher than albite), angles of extinction for twins (Michel-Levy method), 2V, etc. The Michel-Levy method is pretty straightforward to apply. If I really need to know compositions closely (e.g., for petrogenesis, thermobarometry, etc.), I measure them on an electron probe (EPMA) or a well-calibrated scanning electron microscope (SEM). Many plagioclase crystals are zoned, so that complicates determination of compositions.
