Crystal Systems

The seven crystal systems and their characteristic symmetry elements.

Interactive Version

For interactive crystal visualizations and detailed data tables, visit gemmology.dev/learn/crystal-systems.

Overview

All crystals belong to one of seven crystal systems, classified by their unit cell geometry and symmetry elements. Understanding these systems is fundamental to crystallography and gem identification.

Crystal systems are defined by the relationship between crystallographic axes (a, b, c) and the angles between them (α, β, γ). Each system has characteristic symmetry elements that determine possible crystal forms.

The Seven Systems

System	Axes	Angles	Example Gems
Cubic	a = b = c	α = β = γ = 90°	Diamond, Spinel, Garnet
Hexagonal	a₁ = a₂ = a₃ ≠ c	α = β = 90°, γ = 120°	Beryl, Apatite
Trigonal	a₁ = a₂ = a₃ ≠ c	α = β = 90°, γ = 120°	Quartz, Ruby, Tourmaline
Tetragonal	a = b ≠ c	α = β = γ = 90°	Zircon, Rutile
Orthorhombic	a ≠ b ≠ c	α = β = γ = 90°	Topaz, Peridot
Monoclinic	a ≠ b ≠ c	α = γ = 90°, β ≠ 90°	Kunzite, Orthoclase
Triclinic	a ≠ b ≠ c	α ≠ β ≠ γ ≠ 90°	Turquoise, Labradorite

Optic Character

System	Optic Character	RI Values
Cubic	Isotropic	Single RI (n)
Hexagonal, Trigonal, Tetragonal	Uniaxial	Two values (ω, ε)
Orthorhombic, Monoclinic, Triclinic	Biaxial	Three values (α, β, γ)

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Data source: learn/crystal-systems.yaml