For trigonal space groups, symmetry equivalents do not seem as " natural " as in other systems.
It occurs in drusy crusts composed of minute trigonal crystals.
The "trapezohedral," or "plagihedral," faces x {41a} belong to a trigonal trapezohedron.
The bisphenoids (the hemihedral forms of the tetragonal and rhombic bipyramids)., and the trigonal pyramid of the hexagonal system, are examples of non-regular tetrahedra (see Crystallography).
The six small faces s{412} situated on alternate corners at each end of the crystal, are called the "rhomb" faces, because of their shape; if extended they would give a trigonal bipyramid.
There are actually three different ways in which you could arrange 3 bonding pairs and 2 lone pairs into a trigonal bipyramid.
This is in conflict with the trigonal pyramidal geometry predicted by VSEPR theory.
Three groups of electrons around an atom X, always give a trigonal planar arrangement around the central atom X-.
X-ray diffraction studies show it has the expected trigonal bipyramidal structure in the solid state.