A regular 20-faced polyhedron.
However, in global grid systems, the most useful icosahedron is a truncated form which more easily represents the Earth. In the truncated form, the points of the triangle faces are removed, creating central pentagon shapes surrounded by hexagons.
PYXIS uses the truncated icosahedron. To ensure that the tiling works on the polyhedron's surface, the pentagons are considered hexagons with a one-sixth gap. In the unfolded icosahedron, gaps in the northern hemisphere face north, and gaps in the southern hemisphere face south.