disphenoid
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English[edit]
Etymology[edit]
From di- (“twice, double”) + sphenoid (“wedge-shaped crystal or bone of the skull”).
Adjective[edit]
disphenoid (not comparable)
- (mineralogy) Of or pertaining to a wedge-shaped crystal form of the tetragonal or orthorhombic system.
- (mineralogy) Of or pertaining to a crystal form bounded by eight scalene triangles arranged in pairs, constituting a tetragonal scalenohedron.
Noun[edit]
disphenoid (plural disphenoids)
- (geometry) A non-regular tetrahedron whose four faces are congruent acute-angled triangles.
- 1949, Edward Salisbury Dana, Minerals and How to Study Them[1], page 32:
- The mineral chalcopyrite commonly crystallizes in disphenoids that are very difficult to distinguish from tetrahedrons.
- 1973, H. S. M. Coxeter, 3rd Edition, unnumbered page,
- To make a model of a disphenoid, cut out an acute angled triangle and fold it along the joins of the mid-points of the sides. The disphenoid is said to be rhombic or tetragonal according as the triangle is isosceles or scalene.
- 1977, Elizabeth A. Wood, Crystals and Light: An Introduction to Optical Crystallography, Revised edition, page 8:
- If you rotate the [tetragonal] disphenoid 90° around its 2-fold axis and then perform the operation of inversion through the center-point of the object, it will occupy its original position again.
- 1993, Horst Martini, “A Hierarchical Classification of Euclidean Polytopes with Regularity Properties”, in Tibor Bisztriczky, Peter McMullen, Rolf Schneider, Asia Ivic Weiss, editors, Polytopes: Abstract, Convex and Computational, Proceedings of the NATO Advanced Study Institute, page 83:
- In addition it should be remarked that there are two types of disphenoids, with different symmetries: the tetragonal disphenoid (having isosceles facets) and the rhombic one.
Synonyms[edit]
- (non-regular tetrahedron with congruent faces): bisphenoid, equifacial tetrahedron, isosceles tetrahedron