Medieval Alchemists called the Star [of David] the “Philosopher’s stone,” adding a tiny dot on the upper right hand point to represent the presence of God and guidance of the Divine Spirit.
– The Archetypal Mandala of the Star of David, by Margaret Starbird, Gaiamind.com
In some alchemic writings the philosopher’s stone is symbolized as a circle enclosing a hexagonal star (“the star of David”): the circle alludes to the kabbalistic *Ein-Sof (“Infinite”); the triangle which points upward represents the element fire; and the one which points downward the element water. Fire and water together constitute heaven (shamayim = esh + mayim).
From the 17th century, this was used by alchemists to symbolize the primeval matter out of which the main element of the philosopher’s stone, philosophic mercury, the “quintessence,” is extracted.
– ALCHEMY, Bernard Suler, Encyclopaedia Judaica, JewishVirutalLibrary.com