"Zat" is a term used to express a very special quality of turquoise. It is difficult to define but may be considered as similar to describing "water" or "brilliance" in a diamond or "luster" in a pearl. Its one of those situations of "I can"t describe it but I know it when I see it." In this video Mike shows some examples of "zat" in turquoise. One correction to video. Turquoise may have been discovered in Egypt as early as 5000 BC.