What is a window ?
Windowed quartz : definition
A window in gemology :
In gemology, a window is when the pavilion of the stone is cut in such a way that the light passes through without being reflected... This gives stones that are not very shiny, but helps to lighten the dark color of some gemstones. Some crystals due to their shape do not allow to cut correctly proportioned gemstones and therefore always have a window.
In a rough, a window is a small polished part which makes it possible to appreciate the internal quality of the material.