Crystal System

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crystal system

[¦krist·əl ′sis·təm]
One of seven categories (cubic, hexagonal, tetragonal, trigonal, orthorhombic, monoclinic, and triclinic) into which a crystal may be classified according to the shape of the unit cell of its Bravais lattice, or according to the dominant symmetry elements of its crystal class.

Crystal System


any of the seven groups of crystals obtained when a classification is made according to the symmetry of the unit cell. A system is characterized by the ratios between the a, b, and c axes and by the angles α, β, and γ of the unit cell. The seven systems are cubic (a = b = c; α = β = γ = 90°), tetragonal (a = bc; α = β = γ = 90°), hexagonal (a = bc; α = β = 90°; γ = 120°), trigonal (a = b = c; α = β = γ ≠ 90°), orthorhombic (abc; α = β = γ = 90°), mono-clinic (abc; α = β = γ = 90°; β ≠ 90°), and triclinic (abc; αβγ ≠ 90°). As the broadest classification of crystal symmetry, each crystal system includes several symmetry point groups and Bravais lattices.


Popov, G. M., and I. I. Shafranovskii. Kristallografiia, 5th ed. Moscow, 1972.