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