The Six Crystal Families

All minerals fall into one of six crystal classes based on the ordering of their component elements and polyatomic ions.

Isometric, a=b=c, alpha=beta=gamma=90 degrees

Tetragonal: a=b<>c, alpha, beta, and gamma equal 90 degrees

Orthorhombic: a, b, and c are unequal; alpha, beta, and gamma equal 90 degrees; a=20, b=30, c=40

Hexagonal: a=b<>c; alpha=beta=90 degrees, gamma=120 degrees;

Monoclinic, a, b, and c are unequal; alpha and gamma = 90 degrees, beta does not equal 90 degrees

Triclinic: a,b, and c are unequal; neither alpha, nor beta, nor gamma equal 90 degrees