noun
definition
A polyhedron with twenty faces.
definition
(specifically) A regular icosahedron: one of the Platonic solids, all of whose faces are regular (equilateral) triangles
Examples of icosahedron in a Sentence
This is the icosahedron.
Shown above is an icosahedron of twelve dodecahedral structures surrounding a central dodecahedron; (H 2 O) 130.
F rotates the icosahedron in various ways apparently looking for pentagon based pyramids on the " left " and " right " hand sides.
Stainless steel nickel plated candle holder (20 sides - each side 1811 - see Para 12) shape is called an icosahedron.
This category includes the 13-atom icosahedron, which can be decomposed into twenty tetrahedra sharing a common vertex.
Several of these arise naturally as crystals, and the truncated icosahedron occurs in real life as a football.
The energy is measured relative to the energy of the global minimum icosahedron.
Structure 69C has a vertex atom missing from the underlying Mackay icosahedron like 38A.
Further growth then leads to the next Mackay icosahedron.
In order to see some of these more clearly, 64 of the 280 water molecules have been removed from the water icosahedron.
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).
The distance between adjacent vertices of the icosahedron is 5% longer than the distance between a vertex and the center.
Nevertheless, holding that every dimension has a principle of its own, he rejected the derivation of the elemental solids - pyramid, octahedron, icosahedron and cube - from triangular surfaces, and in so far approximated to atomism.
The first three were certainly known to the Egyptians; and it is probable that the icosahedron and dodecahedron were added by the Greeks.
The equilateral triangle is the basis of the tetrahedron, octahedron and icosahedron.'
The great dodecahedron is determined by the intersections of the twelve planes which intersect the Platonic icosahedron in five of its edges; or each face has the same boundaries as the basal sides of five covertical faces of the icosahedron.
The great icosahedron is the reciprocal of the great stellated dodecahedron.
Each of the twenty triangular faces subtend at the centre the same angle as is subtended by four whole and six half faces of the Platonic icosahedron; in other words, the solid is determined by the twenty planes which can be drawn through the vertices of the three faces contiguous to any face of a Platonic icosahedron.
It is enclosed by 20 triangular faces belonging to the original icosahedron, and 12 pentagonal faces belonging to the coaxial dodecahedron.
The truncated icosahedron is formed similarly to the icosidodecahedron, but the truncation is only carried far enough to leave the original faces hexagons.
It is therefore enclosed by 20 hexagonal faces belonging to the icosahedron, and 12 pentagonal faces belonging to the coaxial dodecahedron.
The truncated dodecahedron is formed by truncating the vertices of a dodecahedron parallel to the faces of the coaxial icosahedron so as to leave the former decagons.
It is enclosed by 20 triangular faces belonging to the icosahedron and 12 decagons belonging to the dodecahedron.
In the " small rhombicosidodecahedron " there are 12 pentagonal faces belonging to the dodecahedron, 20 triangular faces belonging to the icosahedron and 30 square faces belonging to the triacontahedron.
The pentagons belong to a dodecahedron, and 20 triangles to an icosahedron; the remaining 60 triangles belong to no regular solid.
Thus the faces of the cuboctahedron, the truncated cube, and truncated octahedron, correspond; likewise with the truncated dodecahedron, truncated icosahedron, and icosidodecahedron; and with the small and great rhombicosidodecahedra.
The boron skeleton takes the form of a regular icosahedron.