# disphenoid

Definition from Wiktionary, the free dictionary

## 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*, page 32,- The mineral chalcopyrite commonly crystallizes in
**disphenoids**that are very difficult to distinguish from tetrahedrons.

- The mineral chalcopyrite commonly crystallizes in
**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.

- To make a model of a
**1977**, Elizabeth A. Wood,*Crystals and Light: An Introduction to Optical Crystallography*, 2nd 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.

- If you rotate the [tetragonal]
**1993**, Horst Martini,*A Hierarchical Classification of Euclidean Polytopes with Regularity Properties*, 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.

- In addition it should be remarked that there are two types of

#### Synonyms[edit]

- (non-regular tetrahedron with congruent faces): bisphenoid, equifacial tetrahedron, isosceles tetrahedron