Billietite is a uncommon mineral of Uranium that contains Barium. It has the chemical formula: Ba(UO₂)₆O₄(OH)₆•8H₂O. It usually occurs as clear yellow orthorhombic crystals. Billietite is named after Valere Louis Billiet (1903-1944), Belgian crystallographer at the University of Ghent, Ghent, Belgium.