"Hieros gamos"--which means "sacred union" or "holy marriage"--is an archtypal idea that occurs in many cultures and contexts, throughout history. In paganism, the hieros gamos is represented by the sexual union of a god or goddess with a mortal man or woman. For the medieval alchemists, the King and Queen were often used as symbols of sun and moon, as shown in this emblem from the famous alchemical manuscript Rosarium Philosophorum.
The union of the King and Queen could result in the production of the Hermaphrodite or Divine Androgyne--"half and half," like the mita y mita described by Anzaldúa. The article "Spritual Alchemy" by Karen-Claire Voss offers a wonderful overview, with lots of illustrations. There is also an excellent introduction to the many facets of alchemy at Adam McLean's comprehensive website.