The icosahedron corresponds to water. It has been known since ancient times. The Icosahedron belongs to 5.3.2 have links to the five elements and the trinities and dualities. Thus they correspond closer to the whole system than the more material elements, which deal with just the four elements. The icosahedron can be inscribed in the octahedron if its vertices are placed on the octahedron-edges in the golden ratio.