Concreciones silicocarbonáticas en basaltos alterados en el área de Praguaniyeu (prov. de Río Negro).
The alteration producís in vugs of the basaltic lavas in Praguaniyeu area (Prov. of Río Negro) were studied by means of polarizaron microscope, XRD, SEM and EDAX. Two associations of alteration were determined, a carbonatic and ferric one, and both accompanied with rather abundant cryptocristaline silica (tridimite and cristobalite).