orthorhombic

Elements with an orthorhombic crystalline structure include boron, oxygen (alpha form), phosphorus (black form), sulfur (alpha form), chlorine (orthorhombic form), gallium (three forms, one of which is a metastable form), bromine, iodine, dysprosium (orthorhombic form), terbium (orthorhombic form), uranium (alpha form), neptunium (alpha form), and plutonium (gamma form).