Resumen de Descripción de la macla de la frondelita-rockbridgeita asociada a las pegmatitas del Macizo de L´Arize, Pirineos (Ariege).

François Fontan, Encarnación Roda Robles

• A cruciform intergrowth in a phosphate of the frondelite-rockbridgeite series associated with beryl-columbite pegmatites is studied on the basis of geometric considerations. The crystallographical calculations prove, for the first time, the existence of a reticular pseudomeroedric twinning in frondelite, having as twin plane the (041), an obliquity of =3 and a twin index =7, which may explain the rarity of this twinning.