the present invention is directed to a method for synthesizing fluorine - containing , aluminosilicate crystals having a stoichiometry approximating that of topaz . the method comprises three basic steps : vapors of a readily - oxidizable compound of silicon and of a readily - oxidizable compound of aluminum and fluorine are passed to a flame oxidation burner ; amorphous fluorine - containing , aluminosilicate particles resulting from the combustion of those gases are collected ; and the collected particles are sintered into an integral body at a temperature between about 650 °- 925 ° c .