Palygorskite and sepiolite occurrences and deposits are frequent in the Iberian Peninsula, mainly in the Tagus basin, in central Spain and Portugal (Galán & Castillo, 1984).
In Portugal, the first palygorskite occurrence was reported by Carvalho (1964) in the region of Ponte do Sor, Tagus basin, in Paleogene sediments. Later, Carvalho (1968) reported palygorskite occurrences in coarse detrital sediments that were occasionally carbonatic or hardened by silicification, and built up the Cenozoic base for the Tagus and Sado basins. Carvalho referred to such formations as the 'Attapulgite complex'. Overlying this attapulgite complex is the 'Montmorillonite complex', probably of Miocene age.