Medial rhombic triacontahedron
In geometry, the medial rhombic triacontahedron (or midly rhombic triacontahedron) is a nonconvex isohedral polyhedron. It is a stellation of the rhombic triacontahedron, and can also be called small stellated triacontahedron. Its dual is the dodecadodecahedron. Its 24 vertices are all on the 12 axes with 5-fold symmetry (i.e. each corresponds to one of the 12 vertices of the icosahedron). This means that on each axis there is an inner and an outer vertex. The ratio of outer to inner vertex radius is , the golden ratio. It has 30 intersecting rhombic faces, which correspond to the faces of the convex rhombic triacontahedron. The diagonals in the rhombs of the convex solid have a ratio of 1 to . The medial solid can be generated from the convex one by stretching the shorter diagonal from length 1 to . So the ratio of rhomb diagonals in the medial solid is 1 to . This solid is to the compound of small stellated dodecahedron and great dodecahedron what the convex one is to the compound of dodecahedron and icosahedron:The crossing edges in the dual compound are the diagonals of the rhombs.The faces have two angles of , and two of . Its dihedral angles equal . Part of each rhomb lies inside the solid, hence is invisible in solid models. (Wikipedia).
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