crystal system

A method of classifying crystalline substances on the basis of their unit cell. There are seven crystal systems. If the cell is a parallelopiped with sides a, b, and c and if α is the angle between b and c, β the angle between a and c, and γ the angle between a and b, the systems are:

(1) cubic a=b=c and α=β=γ=90°
(2) tetragonal a=b≠c and α=β=γ=90°
(3) rhombic (or orthorhombic) a≠b≠c and α=β=γ=90°
(4) hexagonal a=b≠c and α=β=γ=90°
(5) trigonal a=b≠c and α=β=γ≠90°
(6) monoclinic a≠b≠c and α=γ=90°≠β
(7) triclinic a=b=c and α≠β≠γ