A Rowling Stone

Adjacent is the icon of the Deathly Hallows made famous in J. K Rowling's Harry Potter series. The Resurrection Stone (a circle) is inscribed within the Cloak of Invisibility (an equilateral triangle) and the Elder Wand (a vertical line) is drawn on top. 

Supposing the Elder Wand is 18 cm long, what is the area of the Resurrection Stone?