Enneagrammic antiprism

The enneagrammic antiprism, or steap, is a prismatic uniform polyhedron. It consists of 18 triangles and 2 enneagrams. Each vertex joins one enneagram and three triangles. As the name suggests, it is an antiprism based on an enneagram. It is one of three ennegrammic antiprisms, the other two being the great enneagrammic antiprism and the great enneagrammic retroprism.

Vertex coordinates
The vertex coordinates of an enneagrammic antiprism with edge length 2sin(2π/9) are given by: where $$H=\sqrt{\frac{1+2\cos\frac{2\pi}9}{2+2\cos\frac{2\pi}9}}.$$
 * $$\left(1,\,0,\,±H\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{2\pi}{9}\right),\,±\sin\left(\frac{2\pi}{9}\right),\,±H\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{4\pi}{9}\right),\,±\sin\left(\frac{4\pi}{9}\right),\,±H\sin\frac{2\pi}9\right),$$
 * $$\left(-\frac12,\,±\frac{\sqrt3}{2},\,±H\sin\frac{2\pi}9\right),$$
 * $$\left(\cos\left(\frac{8\pi}{9}\right),\,±\sin\left(\frac{8\pi}{9}\right),\,±H\sin\frac{2\pi}9\right),$$