Five 2D lattices Hexagonal a=by=120° Primitive unit cell Five 2D lattices Parallelogram Square Rectangle a a≠bY≠90°， Y≠120° a=by=90° ◆ab”y-90° Primitive unit cellFive 2D lattices a=b γ=120° Primitive unit cell Five 2D lattices a=b γ=90° a≠b γ=90° a≠b γ ≠ 90° , γ ≠ 120° Primitive unit cell