Microscope view of a sanidine crystal from the Lava Creek Tuff (Yellowstone caldera) with geochemical composition indicated for a point measured by electron microprobe analysis

A close-up (microscope) image of a sanidine crystal from the Lava Creek Tuff, which erupted during the formation of Yellowstone Caldera about 631,000 years ago, marked with a point where electron microprobe analysis was performed. The chemistry of that point is given, where each major element has a corresponding weight percent. This chemical makeup is used in thermometry equations to determine the temperature at which the crystal formed in the magma chamber. Photo by Violet Turner, July 15, 2025.