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1A three-dimensional shape having eight plane faces, especially a regular solid figure with eight equal triangular faces.
‘I'd like to mention in passing that the octahedron, the dual of the cube, also contains 26: 8 faces, 12 edges, 6 vertices.’
‘There is the octahedron, with 8 faces, 12 edges and 6 vertices.’
‘This six-point perspective, with the six vertices of an octahedron serving as the vanishing points, becomes the basis of his spherical paintings.’
‘These are often known as the Platonic solids: the tetrahedron, cube, octahedron, dodecahedron and icosahedron.’
‘Plato believed that atoms have the shapes of regular polyhedra: cubes, tetrahedrons, octahedrons, and so on.’
‘Peterson and Jordan go on to investigate interesting links between integer octahedra and integer antiprisms.’
‘A dodecahedron modified by the octahedron and cube from Nordmark, Sweden, is figured in Goldschmidt.’
‘The cube, consisting of six square faces, is a common form either alone or in combination with other forms, especially the octahedron.’
‘It was a set of platonic bodies: there was an octahedron and a double tetrahedron.’
‘Finally, the octahedron inscribed in the Venus-orbit sphere has itself an inscribed sphere, on which the orbit of Mercury lies.’
‘These five remarkable solids - tetrahedron, cube, octahedron, dodecahedron, icosahedron - have faces that are congruent equilateral polygons.’
‘Theaetetus was the first to study the octahedron and the icosahedron and it is believed that Book XIII of Euclid's Elements is based on his work.’
1.1A body, especially a crystal, in the form of a regular octahedron.
‘The exception is an octahedron from another Peruvian mine, Quiruvilca (400 kilometers north of Huanzala).’
‘The Ogluinsky mine specimens are millimeter-sized octahedra, and the Nicolay mine specimens are unabraded and have mica attached.’
‘When well-crystallized, it typically exhibits the cube form modified by the octahedron and dodecahedron; crystals to 20 cm across have been reported.’
‘There were smoky quartz crystals plus huge fluorite octahedra.’
‘It involves placing the knot inside a plastic octahedron and mapping where the strands of the knot meet.’
‘Most that I have seen have been elongated octahedra or other forms, such as some of the branches of an arborescent aggregate.’
‘Most of these specimens exhibit crystals that are cubic in habit; however, octahedra of both blue-gray and medium green have also been common.’
‘In contrast to crystals that resemble textbook drawings, the most frequently encountered gold crystals are skeletal octahedra.’
‘The one exception is the exciting accidental discovery of a 4.22-carat, gem-quality octahedron in Dale County, Alabama.’
‘Copper, Cu, has been found associated with cuprite octahedra at Pedra Preta, where these minerals occur on talc and magnesite.’
‘A diamond crystal is essentially two pyramids stuck together - an octahedron.’
‘The octahedra range from 5 to 10 pm in diameter and show interpenetrant growth.’
‘Earth was a cube, air an octahedron, fire a tetrahedron and water an icosahedron.’
‘Water was an icosahedron, and air had to be an octahedron.’
‘She notes that lime-green to purplish-green modified fluorite octahedra have been found at this pegmatite.’
‘One small lot of specimens from Alta Floresta, Mato Grosso, exhibited moderately rounded, well-developed octahedra.’
‘One specimen was covered with small rounded crystal-like projections, similar to cube and octahedron forms.’
‘Older collections sometimes contain small, very pale, transparent green fluorite octahedra from the Tomboy vein.’
‘While writing, I may choose a clear Quartz Crystal for clarity or a yellow Fluorite octahedron to help keep creative thoughts flowing.’
‘The fluorite tends to occur only as cubes modified by the dodecahedron, with simple cubes or octahedra uncommon or absent.’
Origin
Late 16th century: from Greek oktaedron, neuter (used as a noun) of oktaedros ‘eight-faced’.