Spatial rank and approximate symmetries in sequential reconstruction of dense packings

Glasses containing fluorine. These glasses are characterized by the fact that they contain at least 25% in moles, approximately, of a fluoride or a mixture of fluorides MX(X1)2, in which: X and X1 each represent a fluorine atom, and M then represents a metal chosen from among the group consisting of gallium, iron, chromium, vanadium, indium, and the rare earths, or X represents an oxygen atom, X1 represents a fluorine atom, and M then represents a titanium atom, it being understood that the said glasses contain no hydrofluoric acid as a network former and that, in the case in which M represents a gallium or indium atom, the glasses do not contain more than 15% in moles of BaPO3F. Application notably in obtaining glasses containing various cations conferring particular optical or magneto-optical properties.