An investigation of the orthorhombic crystal topaz, Al2SiO4F2, with x-rays has been reported by Leonhardt. With the aid of data from Laue and rotation photographs he found for the edges of the unit of structure, containing 4Al2SiO4F2, the values d100 = 4.64 A, d010 = 8.78 A, and d001 = 8.37 A, and determined the space-group of the crystal to be V16h. A deduction of the atomic arrangement, dependent on about fifteen parameters, was not attempted; for such complicated structures cannot be treated by the usual methods.