Johnson Solids (Page 1)

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(J12) Triangular Dipyramid
regular faces
Vertices:  5  (2[3] + 3[4])
Faces:6  (6 equilateral triangles)
Edges:9
Symmetry:  3-fold Prismatic  (D3h)
(values below based on edge length = 1)
Inscribed Radius:  sqrt(6)/9    ≈0.27216552697590867758
Volume:sqrt(2)/6    ≈0.23570226039551584147