Editing Deltahedron (section)

{{short description|Polyhedron made of equilateral triangles}}
{{distinguish|Deltohedron|text="[[Deltohedron]]", a term sometimes used to refer to the set of trapezohedra}}

A '''deltahedron''' is a [[polyhedron]] whose faces are all [[equilateral triangle]]s. The deltahedron was named by [[Martyn Cundy]], after the Greek capital letter [[Delta (letter)|delta]] resembling a triangular shape Δ.<ref>{{multiref
|{{harvp|Cundy|1952}}
|{{harvp|Cromwell|1997|p=[https://archive.org/details/polyhedra0000crom/page/75/mode/1up 75]}}
|{{harvp|Trigg|1978}}
}}</ref>

Deltahedra can be categorized by the property of [[Convex set|convexity]]. The simplest convex deltahedron is the [[regular tetrahedron]], a pyramid with four equilateral triangles. There are eight convex deltahedra, which can be used in the applications of chemistry as in the [[polyhedral skeletal electron pair theory]] and [[chemical compound]]s. There are infinitely many concave deltahedra.