Underground exposures at the Tanco mine reveal the complexities of texture and mineral-chemical zonation that have made pegmatites such an enigmatic and interesting group of rocks. Here, banded albitic aplites grade upward into a thin band of nearly pure tantalum oxide minerals (thin dark band at the edge of the aplite), followed by very coarse-grained cesian beryl and finally massive gray quartz. These textures and mineral assemblages could not easily be reconciled with their igneous origin until I advanced the model for disequilibrium crystallization that produces sequential textures and compositions such as these. This photo is courtesy of Petr Cerny.