Hemi-icosahedron

In geometry, a hemi-icosahedron is an abstract regular polyhedron, containing half the faces of a regular icosahedron. It can be realized as a projective polyhedron, which can be visualized by constructing the projective plane as a hemisphere where opposite points along the boundary are connected and dividing the hemisphere into three equal parts.

Geometry

It has 10 triangular faces, 15 edges, and 6 vertices.
It is also related to the nonconvex uniform polyhedron, the tetrahemihexahedron, which could be topologically identical to the hemi-icosahedron if each of the 3 square faces were divided into two triangles.

Graphs

It can be represented symmetrically on faces, and vertices as Schlegel diagrams:

The complete graph K6

It has the same vertices and edges as the 5-dimensional 5-simplex which has a complete graph of edges, but only contains half of the faces.
From the point of view of graph theory this is an embedding of on a real projective plane. With this
embedding, the dual graph is the Petersen graph --- see hemi-dodecahedron.