What is a twin structure? An answer from microcline minerals from pegmatites

Twin-structures in microcline specimens from granite pegmatites were studied by polarized light microscopy (PLM) and Raman microprobe (RMP) spectra. Ordinary and diagonal Albite-Pericline orientation variants from transformation twinning (after a monoclinic precursor) and subsequent solid-state recrystallization twinning were observed. They exhibit a “complexity”, related to the particular organizations of the twin units, that is totally expected from traditional crystallographic and equilibrium thermodynamic views. They evolve as global entities with adaptation capabilities to the geological environment. Twin-structure formation involves the active participation of the electron lattices as a fundamental feature of the crystalline state.