2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/147540We present for the first time the evidence for a thermodynamically stable incommensurate elongated-triangle ($ELT$) phase in quartz observed by transmission electron microscopy at structural $α-β$ transition. The phase sequence on cooling is: uniform $β$ phase - stripe incommensurate phase (ferroelastic) - incommensurate equilateral-triangle ($EQT$) phase (ferroelectric) - incommensurate $ELT$ (ferroelectric and ferroelastic) - uniform $α$ phase. The $ELT$ blocks could be responsible for the large light scattering in the vicinity of $α-β$ transition.4 pages revtex file +3 uuencoded compressed postscript figuresCondensed Mattertext