The trigonal crystal system is defined by a three-fold rotation axis, and can be generated from the cubic crystal system by stretching the cube along its diagonal. The symmetry requires the primitive vectors to have the form a=b, α=β=π/2, γ=120∘.

What makes a crystal trigonal?

The trigonal unit cell is distinguished by the presence of a single line called an axis of three-fold symmetry about which the cell can be rotated by 120° to produce a face indistinguishable from the face presented in the starting position. ... Selenium and other elements may crystallize in trigonal form.

Is trigonal and triclinic same?

As adjectives the difference between triclinic and trigonal

is that triclinic is (crystallography) having three unequal axes all intersecting at oblique angles while trigonal is symmetrically triangular.