A mineral of the mottramite-descloizite series from the Blanquita deposit (Los Menucos, Province of Río Negro), was studied by means of X-ray diffiraction, petrographic microscope and SEM-EDX analysis. The mineral occur as well developed transparent crystals with bright yellow colours and yellowish surficial films. The kaolinic mineralization in Blanquita quarry occurred within the Sierra Colorada Formation (riolitic tuff).