People choose the crystals used in the grids intuitively as well as by the traditional use of a stone.Grids are often made with clear quartz crystals alone . Other grids use a combination of quartz and other stones and crystals and some may not use clear quartz at all. some will be entirely of one kind of stone and some may use dozens of different stones. Intuition ,need and purpose as well as what stones are available to you will determine what you use in a grid.