# Icosahedron

**ICOSAHEDRON** (Gr. eiro<n, twenty, and '(Spa, a face or base), in geometry, a solid enclosed by twenty faces. The " regular icosahedron
" is one of the Platonic solids; the " great icosahedron " is a Kepler-Poinsot solid; and the " truncated icosahedron " is an Archimedean solid (see
POLYHEDRON). In crystallography the icosahedron is a possible form, but it has not been observed; it is closely simulated by a combination of the octahedron and
pentagonal dodecahedron, which has twenty triangular faces, but only eight are equilateral, the remaining twelve being isosceles (see CRYSTALLOGRAPHY).

*Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)*